[CMake] Fixes using CMake 3.27.0.

Testing libc++ with CMake 3.27.0-rc1 fails. It seems some of the modules
used in CMake are not included.

The error before this change was
```
CMake Error at <mono-repo>/llvm/cmake/modules/HandleLLVMOptions.cmake:821 (CHECK_C_SOURCE_COMPILES):
  Unknown CMake command "CHECK_C_SOURCE_COMPILES".
Call Stack (most recent call first):
  CMakeLists.txt:156 (include)
```

Reviewed By: thesamesam

Differential Revision: https://reviews.llvm.org/D152619