[VE] Support multiple architectures installation

Change C++ header files placement to support multiple LLVM_RUNTIME_TARGETS
build.  Also modifies regression test for it.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D114527

GitOrigin-RevId: 83f572527e0fcc1cd0be8ee23bc12abf27027daf
6 files changed