[flang] Remove `%f18` from LIT configuration files

[awarzynski]

Summary

%f18 was originally introduced to represent the old Flang driver,
f18. With the introduction of the new driver, flang-new, we have
been switching to %flang (compiler driver) and %flang_fc1 (frontend
driver) as more generic alternatives.

As most tests have been portend to use the new LIT variables instead of
%f18, this is good time to remove it from lit.cfg.py. There's only one
test left that requires the old driver to run. It's updated with:

! REQUIRES: old-flang-driver

This way we preserve its semantics while reducing the number of
variables in LIT configuration.

[arnamoy10]

flang/test/lit.cfg.py

67

Can we remove this variable or we envision some future uses of this?

[awarzynski]

flang/test/lit.cfg.py

67

Not really, tool is used on lines 79 and 81.

[arnamoy10]

LGTM

flang/test/lit.cfg.py

67

I see, thanks!

[Leporacanthicus]

LGTM

flang/test/Driver/help-f18.f90

-! RUN: %f18 -h 2>&1 | FileCheck %s
-! RUN: %f18 -help 2>&1 | FileCheck %s
-! RUN: %f18 --help 2>&1 | FileCheck %s
-! RUN: %f18 -? 2>&1 | FileCheck %s
+! REQUIRES: old-flang-driver
+
+! RUN: %flang -h 2>&1 | FileCheck %s
+! RUN: %flang -help 2>&1 | FileCheck %s
+! RUN: %flang --help 2>&1 | FileCheck %s
+! RUN: %flang -? 2>&1 | FileCheck %s
 
 ! CHECK: f18: LLVM Fortran compiler
 
 ! CHECK:   -help                print this again
 ! CHECK: Unrecognised options are passed through to the external compiler
 ! CHECK: set by F18_FC (see defaults).

flang/test/lit.cfg.py

 # subdirectories contain auxiliary inputs for various tests in their parent
 # directories.
 config.excludes = ['Inputs', 'CMakeLists.txt', 'README.txt', 'LICENSE.txt']
 
 # If the new Flang driver is enabled, add the corresponding feature to
 # config.
 if config.include_flang_new_driver_test:
   config.available_features.add('new-flang-driver')
+else:
+  config.available_features.add('old-flang-driver')
 
 # test_source_root: The root path where tests are located.
 config.test_source_root = os.path.dirname(__file__)
 
 # test_exec_root: The root path where tests should be run.
 config.test_exec_root = os.path.join(config.flang_obj_root, 'test')
 
 # Tweak the PATH to include the tools dir.
 llvm_config.with_environment('PATH', config.flang_tools_dir, append_path=True)
 llvm_config.with_environment('PATH', config.llvm_tools_dir, append_path=True)
 
 if config.flang_standalone_build:
     # For builds with FIR, set path for tco and enable related tests
     if config.flang_llvm_tools_dir != "":
         config.available_features.add('fir')
         if config.llvm_tools_dir != config.flang_llvm_tools_dir:
             llvm_config.with_environment('PATH', config.flang_llvm_tools_dir, append_path=True)
 
 # For each occurrence of a flang tool name, replace it with the full path to
 # the build directory holding that tool.
-tools = [
-  ToolSubst('%f18', command=FindTool('f18'),
-    unresolved='fatal')
-]
-
+tools = []
 if config.include_flang_new_driver_test:
    tools.append(ToolSubst('%flang', command=FindTool('flang-new'), unresolved='fatal'))
    tools.append(ToolSubst('%flang_fc1', command=FindTool('flang-new'),
     extra_args=['-fc1'], unresolved='fatal'))
 else:
    tools.append(ToolSubst('%flang', command=FindTool('f18'),
     unresolved='fatal'))
    tools.append(ToolSubst('%flang_fc1', command=FindTool('f18'),