[cmake] Move HandleOutOfTreeLLVM to common cmake utils

This is better than libunwind and libcxxabi fishing it out of libcxx's
module directory.

It is done in prepartion for a better version of D117537 which deduplicates
CMake logic instead of just renaming to avoid a name clash.

Reviewed By: phosek, #libunwind, #libc_abi, Ericson2314

Differential Revision: https://reviews.llvm.org/D117617

NOKEYCHECK=True
GitOrigin-RevId: 429a717ea5ec141b5c0c93c2c53097dccf67e05a
1 file changed
tree: 1103f06d0a2b810fbceb3fb8be063ca4879a5949
  1. cmake/
  2. docs/
  3. include/
  4. src/
  5. test/
  6. .clang-format
  7. CMakeLists.txt
  8. LICENSE.TXT