[compiler-rt] Fix CMake configure on Windows (#90843)

CMake configure compiler-rt got broken as a result of following commit:
d3925e65

This patch fixes the break by porting the above commit for clang-cl.

This problem was not caught on Windows buildbots beacuase it appeared
when compiler-rt was included via LLVM_ENABLE_PROJECTS while buildbots
include compiler-rt project using LLVM_ENABLE_RUNTIMES flag.