[all-commits] [llvm/llvm-project] c4c388: build: use `find_package(Python3)` if available

[Saleem Abdulrasool via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: c4c3883b00d3a6aa657a5e3e515c90c9ea1f81c6
      https://github.com/llvm/llvm-project/commit/c4c3883b00d3a6aa657a5e3e515c90c9ea1f81c6
  Author: Saleem Abdulrasool <compnerd at compnerd.org>
  Date:   2020-04-28 (Tue, 28 Apr 2020)

  Changed paths:
    M clang-tools-extra/test/lit.site.cfg.py.in
    M clang/CMakeLists.txt
    M clang/bindings/python/tests/CMakeLists.txt
    M clang/test/lit.site.cfg.py.in
    M clang/utils/perf-training/CMakeLists.txt
    M clang/utils/perf-training/lit.site.cfg.in
    M clang/utils/perf-training/order-files.lit.site.cfg.in
    M lld/CMakeLists.txt
    M lld/test/Unit/lit.site.cfg.py.in
    M lld/test/lit.site.cfg.py.in
    M llvm/CMakeLists.txt
    M llvm/cmake/config-ix.cmake
    M llvm/cmake/modules/AddLLVM.cmake
    M llvm/test/lit.site.cfg.py.in
    M llvm/tools/llvm-shlib/CMakeLists.txt

  Log Message:
  -----------
  build: use `find_package(Python3)` if available

This is primarily motivated by the desire to move from Python2 to
Python3.  `PYTHON_EXECUTABLE` is ambiguous.  This explicitly identifies
the python interpreter in use.  Since the LLVM build seems to be able to
completed successfully with python3, use that across the build.  The old
path aliases `PYTHON_EXECUTABLE` to be treated as Python3.