[flang][driver] Remove references to the `flang` bash script

[awarzynski]

Summary

This is a follow-up of https://reviews.llvm.org/D125832
(see also https://reviews.llvm.org/D125788 for more context). It simply
removes any remaining references to the flang bash script. Note that
that flang-to-external-fc remains intact.

[DavidSpickett]

Is it worth updating flang/docs/ReleaseNotes.md ? Though it seems to have been abandoned.

flang/tools/f18/flang-to-external-fc

2

flang-to-external-fc te -> to

[awarzynski]

Fix typo, update release notes

[DavidSpickett]

LGTM

[awarzynski]

In D127094#3559834, @DavidSpickett wrote:

Is it worth updating flang/docs/ReleaseNotes.md ? Though it seems to have been abandoned.

It is, updated :) I removed all of the old stuff - that was written for LLVM 12 and should've been cleared ages ago.

flang/docs/FlangDriver.md

.. contents::
    :local:
 ```
 
 There are two main drivers in Flang:
 * the compiler driver, `flang-new`
 * the frontend driver, `flang-new -fc1`
 
 > **_NOTE:_** The diagrams in this document refer to `flang` as opposed to
-> `flang-new`. This is because the diagrams reflect the final design that we
-> are still working towards. See the note on [the flang script](https://github.com/llvm/llvm-project/blob/main/flang/docs/FlangDriver.md#the-flang-script)
-> below for more context.
+> `flang-new`. Eventually, `flang-new` will be renamed as `flang` and the
+> diagrams reflect the final design that we are still working towards.
 
 The **compiler driver** will allow you to control all compilation phases (e.g.
 preprocessing, semantic checks, code-generation, code-optimisation, lowering
 and linking). For frontend specific tasks, the compiler driver creates a
 Fortran compilation job and delegates it to `flang-new -fc1`, the frontend
 driver. For linking, it creates a linker job and calls an external linker (e.g.
 LLVM's [`lld`](https://lld.llvm.org/)). It can also call other tools such as
 external assemblers (e.g. [`as`](https://www.gnu.org/software/binutils/)). In

 invoking the compiler driver, `flang-new`, with the `-fc1` flag.
 
 The frontend driver will only run one action at a time. If you specify multiple
 action flags, only the last one will be taken into account. The default action
 is `ParseSyntaxOnlyAction`, which corresponds to `-fsyntax-only`. In other
 words, `flang-new -fc1 <input-file>` is equivalent to `flang-new -fc1 -fsyntax-only
 <input-file>`.
 
-## The `flang` script
-The `flang` wrapper script for `flang-new` was introduced as a development tool
-and to facilitate testing. While code-generation is not available in Flang, you
-can use it as a drop-in replacement for other Fortran compilers in your build
-scripts.
-
-The `flang` wrapper script will:
+## The `flang-to-external-fc` script
+The `flang-to-external-fc` wrapper script for `flang-new` was introduced as a
+development tool and to facilitate testing. The `flang-to-external-fc` wrapper
+script will:
 * use `flang-new` to unparse the input source file (i.e. it will run `flang-new
   -fc1 -fdebug-unparse <input-file>`), and then
 * call a host Fortran compiler, e.g. `gfortran`, to compile the unparsed file.
 
-Here's a basic breakdown of what happens inside `flang` when you run `flang
-file.f90`:
+Here's a basic breakdown of what happens inside `flang-to-external-fc` when you
+run `flang-to-external-fc file.f90`:
 ```bash
 flang-new -fc1 -fdebug-unparse file.f90 -o file-unparsed.f90
 gfortran file-unparsed.f90
 ```
 This is a simplified version for illustration purposes only. In practice,
-`flang` adds a few more frontend options and it also supports various other use
-cases (e.g. compiling C files, linking existing object files). `gfortran` is
-the default host compiler used by `flang`. You can change it by setting the
-`FLANG_FC` environment variable.
-
-Our intention is to replace `flang` with `flang-new`. Please consider `flang`
-as a temporary substitute for Flang's compiler driver while the actual driver
-is in development.
+`flang-to-external-fc` adds a few more frontend options and it also supports
+various other use cases (e.g. compiling C files, linking existing object
+files). `gfortran` is the default host compiler used by `flang-to-external-fc`.
+You can change it by setting the `FLANG_FC` environment variable.
 
 ## Adding new Compiler Options
 Adding a new compiler option in Flang consists of two steps:
 * define the new option in a dedicated TableGen file,
 * parse and implement the option in the relevant drivers that support it.
 
 ### Option Definition
 All of Flang's compiler and frontend driver options are defined in

flang/docs/ReleaseNotes.md

-# Flang 12.0.0 (In-Progress) Release Notes
+# Flang 15.0.0 (In-Progress) Release Notes
 
 > **warning**
 >
-> These are in-progress notes for the upcoming LLVM 12.0.0 release.
+> These are in-progress notes for the upcoming LLVM 15.0.0 release.
 > Release notes for previous releases can be found on [the Download
 > Page](https://releases.llvm.org/download.html).
 
 ## Introduction
 
 This document contains the release notes for the Flang Fortran frontend,
-part of the LLVM Compiler Infrastructure, release 12.0.0. Here we
+part of the LLVM Compiler Infrastructure, release 15.0.0. Here we
 describe the status of Flang in some detail, including major
 improvements from the previous release and new feature work. For the
 general LLVM release notes, see [the LLVM
 documentation](https://llvm.org/docs/ReleaseNotes.html). All LLVM
 releases may be downloaded from the [LLVM releases web
 site](https://llvm.org/releases/).
 
 Note that if you are reading this file from a Git checkout, this
 document applies to the *next* release, not the current one. To see the
 release notes for a specific release, please see the [releases
 page](https://llvm.org/releases/).
 
-## Known Issues
+## Major New Features
 
-These are issues that couldn't be fixed before the release. See the bug
-reports for the latest status.
+## Bug Fixes
 
- *   ...
+## Non-comprehensive list of changes in this release
+* The bash wrapper script, `flang`, is renamed as `flang-to-external-fc`.
 
-## Introducing Flang
+## New Compiler Flags
 
-Flang is LLVM's Fortran front end and is new for the LLVM 11 release.
+## Windows Support
 
-Flang is still a work in progress for this release and is included for
-experimentation and feedback.
+## Fortran Language Changes in Flang
 
-Flang is able to parse a comprehensive subset of the Fortran language
-and check it for correctness. Flang is not yet able to generate LLVM IR
-for the source code and thus is unable to compile a running binary.
+## Build System Changes
 
-Flang is able to unparse the input source code into a canonical form and
-emit it to allow testing. Flang can also invoke an external Fortran
-compiler on this canonical input.
+## New Issues Found
 
-Flang's parser has comprehensive support for:
- * Fortran 2018
- * OpenMP 4.5
- * OpenACC 3.0
-
-Interested users are invited to try to compile their Fortran codes with
-flang in and report any issues in parsing or semantic checking in
-[bugzilla](https://bugs.llvm.org/enter_bug.cgi?product=flang).
-
-### Major missing features
-
- * Flang is not supported on Windows platforms.
-
-## Using Flang
-
-Usage: `flang hello.f90 -o hello.bin`
-
-By default, Flang will parse the Fortran file `hello.f90` then unparse it to a
-canonical Fortran source file. Flang will then invoke an external
-Fortran compiler to compile this source file and link it, placing the
-resulting executable in `hello.bin`.
-
-To specify the external Fortran compiler, set the `F18_FC` environment
-variable to the name of the compiler binary and ensure that it is on your
-`PATH`. The default value for `F18_FC` is `gfortran`.
-
-When invoked with no source input, Flang will wait for input on stdin.
-When invoked in this way, Flang performs the same actions as if
-called with `-fdebug-measure-parse-tree -funparse` and does not invoke
-`F18_FC`.
-
-For a full list of options that Flang supports, run `flang --help`.
 
 ## Additional Information
 
 Flang's documentation is located in the `flang/docs/` directory in the
 LLVM monorepo.
 
 If you have any questions or comments about Flang, please feel free to
 contact us via the [mailing
 list](https://lists.llvm.org/mailman/listinfo/flang-dev).

flang/tools/f18/CMakeLists.txt

 # This flang shell script will only work in a POSIX shell.
 if (NOT WIN32)
   add_custom_command(
     OUTPUT ${CMAKE_BINARY_DIR}/bin/flang-to-external-fc
     DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/flang-to-external-fc
     COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/flang-to-external-fc ${CMAKE_BINARY_DIR}/bin)
   add_custom_target(flang-to-external-fc ALL DEPENDS ${CMAKE_BINARY_DIR}/bin/flang-to-external-fc)
   install(PROGRAMS ${CMAKE_BINARY_DIR}/bin/flang-to-external-fc DESTINATION "${CMAKE_INSTALL_BINDIR}")
-  add_custom_target(flang-slink ALL DEPENDS ${CMAKE_BINARY_DIR}/bin/flang-to-external-fc COMMAND ${CMAKE_COMMAND} -E create_symlink
-    ${CMAKE_BINARY_DIR}/bin/flang-to-external-fc ${CMAKE_BINARY_DIR}/bin/flang)
-  install(PROGRAMS ${CMAKE_BINARY_DIR}/bin/flang DESTINATION "${CMAKE_INSTALL_BINDIR}")
 endif()
 
 # TODO Move this to a more suitable location
 file(COPY ${FLANG_SOURCE_DIR}/module/omp_lib.h DESTINATION "${CMAKE_BINARY_DIR}/include/flang/OpenMP/" FILE_PERMISSIONS OWNER_READ OWNER_WRITE)

flang/tools/f18/flang-to-external-fc

 #! /usr/bin/env bash
-#===-- tools/f18/flang.sh -----------------------------------------*- sh -*-===#
+#===-- tools/f18/flang-to-external-fc.sh --------------------------*- sh -*-===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===------------------------------------------------------------------------===#
 # A wrapper script for Flang's compiler driver that was developed for testing and
 # experimenting. You should be able to use it as a regular compiler driver. It