[libc] Remove a now uneccesary CMake policy.

[KyleFromKitware]

+1

Any chance we could get the rest of LLVM upgraded to 3.20.0 as well? I'd like to get Ninja Multi-Config working.

[jhuber6]

In D143139#4099766, @KyleFromKitware wrote:

+1

Any chance we could get the rest of LLVM upgraded to 3.20.0 as well? I'd like to get Ninja Multi-Config working.

CMake Warning at CMakeLists.txt:5 (message):

Your CMake version is 3.18.4.  Starting with LLVM 17.0.0, the minimum
version of CMake required to build LLVM will become 3.20.0, and using an
older CMake will become an error.  Please upgrade your CMake to at least
3.20.0 now to avoid issues in the future!

Seems the buildbots need to be updated first.

[sivachandra]

In D143139#4099772, @jhuber6 wrote:

CMake Warning at CMakeLists.txt:5 (message):

Your CMake version is 3.18.4.  Starting with LLVM 17.0.0, the minimum
version of CMake required to build LLVM will become 3.20.0, and using an
older CMake will become an error.  Please upgrade your CMake to at least
3.20.0 now to avoid issues in the future!

Seems the buildbots need to be updated first.

For us, the buildbot builders are the indicators of health. Should we have to block on these pre-commit failures?

[sivachandra]

Remove the CMake version bump as it is being done in
https://reviews.llvm.org/D144509 in a single-shot to
the entire llvm-project.

libc/CMakeLists.txt

 cmake_minimum_required(VERSION 3.13.4)
 
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 
-# Use old version of target_sources command which converts the source
-# file paths to full paths.
-cmake_policy(SET CMP0076 OLD)
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 
 # The top-level sourse and binary directories.
 set(LIBC_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(LIBC_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 # The top-level directory in which libc is being built.
 set(LIBC_BUILD_DIR ${CMAKE_CURRENT_BINARY_DIR})