[cmake] Pass PYTHON_EXECUTABLE to native builds

Ensure that the nested native build uses the same python interpreter as
the main build, in case the python that CMake detects first is not the
python that the user has specified explicitly.

Original fix by Anuj Mittal <[email protected]>.

Author: rossburton

llvm/cmake/modules/CrossCompile.cmake

@@ -101,6 +101,7 @@ function(llvm_create_cross_target project_name target_name toolchain buildtype)
         -DLLVM_INCLUDE_BENCHMARKS=OFF
         -DLLVM_INCLUDE_TESTS=OFF
         -DLLVM_TABLEGEN_FLAGS="${LLVM_TABLEGEN_FLAGS}"
+        -DPYTHON_EXECUTABLE="${PYTHON_EXECUTABLE}"
         ${build_type_flags} ${linker_flag} ${external_clang_dir} ${libc_flags}
         ${ARGN}
     WORKING_DIRECTORY ${${project_name}_${target_name}_BUILD}