[LLVM] Partially revert GPU change to include dirs

Summary:
Turns out that we need this for the header install directory. I didn't
notice because I had old values cached. Revert for now until I think of
a better way to suppress the error.

Author: jhuber6

llvm/cmake/modules/AddLLVM.cmake

@@ -1,7 +1,4 @@
-if(NOT LLVM_RUNTIMES_GPU_BUILD)
-  include(GNUInstallDirs)
-endif()
-
+include(GNUInstallDirs)
 include(LLVMDistributionSupport)
 include(LLVMProcessSources)
 include(LLVM-Config)