[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

GitOrigin-RevId: 429a717ea5ec141b5c0c93c2c53097dccf67e05a
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6b3bcef..78f4864 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,10 +37,6 @@
   set(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
   set(PACKAGE_BUGREPORT "llvm-bugs@lists.llvm.org")
 
-  # Add the CMake module path of libcxx so we can reuse HandleOutOfTreeLLVM.cmake
-  set(LIBCXXABI_LIBCXX_CMAKE_PATH "${LIBCXXABI_LIBCXX_PATH}/cmake/Modules")
-  list(APPEND CMAKE_MODULE_PATH "${LIBCXXABI_LIBCXX_CMAKE_PATH}")
-
   # In a standalone build, we don't have llvm to automatically generate the
   # llvm-lit script for us.  So we need to provide an explicit directory that
   # the configurator should write the script into.