Fix cmake script to allow cross compiling from windows

[datcuandrei]

Summary

separate_arguments would fail whenever there would be a space in CMAKE_C_COMPILER, including on Linux.

According to CMake docs, add_custom_command does not guarantee a bash environment. Currently, this is not a problem on Linux, but on Windows we get cmd.exe trying to execute :. With my changes, bash is executed explicitly and it will work even on windows, provided bash.exe is somewhere in PATH.

compiler-rt/cmake/Modules/AddCompilerRT.cmake

       set(output_file_${libname} ${output_name_${libname}}${CMAKE_C_OUTPUT_EXTENSION})
       foreach(substitution ${substitutions})
         if(substitution STREQUAL "<CMAKE_C_COMPILER>")
-          string(REPLACE "<CMAKE_C_COMPILER>" "${CMAKE_C_COMPILER} ${CMAKE_C_COMPILER_ARG1}"
+          string(REPLACE "<CMAKE_C_COMPILER>" "\"${CMAKE_C_COMPILER}\" ${CMAKE_C_COMPILER_ARG1}"
                  compile_command_${libname} ${compile_command_${libname}})
         elseif(substitution STREQUAL "<OBJECT>")
           string(REPLACE "<OBJECT>" "${output_dir_${libname}}/${output_file_${libname}}"

                  ${compile_command_${libname}})
         endif()
       endforeach()
-      separate_arguments(compile_command_${libname})
+      separate_arguments(compile_command_${libname} NATIVE_COMMAND ${compile_command_${libname}})
       add_custom_command(
           OUTPUT ${output_dir_${libname}}/${output_file_${libname}}
           COMMAND ${compile_command_${libname}}

llvm/cmake/modules/AddLLVM.cmake

     # FIXME: Don't write the "local:" line on OpenBSD.
     # in the export file, also add a linker script to version LLVM symbols (form: LLVM_N.M)
     add_custom_command(OUTPUT ${native_export_file}
-      COMMAND echo "LLVM_${LLVM_VERSION_MAJOR} {" > ${native_export_file}
-      COMMAND grep -q "[[:alnum:]]" ${export_file} && echo "  global:" >> ${native_export_file} || :
-      COMMAND sed -e "s/$/;/" -e "s/^/    /" < ${export_file} >> ${native_export_file}
-      COMMAND echo "  local: *;" >> ${native_export_file}
-      COMMAND echo "};" >> ${native_export_file}
+      COMMAND bash -c "echo 'LLVM_${LLVM_VERSION_MAJOR} {' > ${native_export_file}"
+      COMMAND bash -c "grep -q '[[:alnum:]]' ${export_file} && echo '  global:' >> ${native_export_file} || :"
+      COMMAND bash -c "sed -e 's/$/;/' -e 's/^/    /' < ${export_file} >> ${native_export_file}"
+      COMMAND bash -c "echo '  local: *;' >> ${native_export_file}"
+      COMMAND bash -c "echo '};' >> ${native_export_file}"
       DEPENDS ${export_file}
       VERBATIM
       COMMENT "Creating export file for ${target_name}")