Reland: [clang] Adding Platform/Architecture Specific Resource Header Installation Targets

The goal of this patch is to improve distribution build's flexibility to include only applicable header files.

Currently, the clang-resource-headers target contains nearly all the files in clang/lib/Headers. Most of these files are platform specific (e.g. immintrin.h is x86 specific). A distribution build will have to either include all the headers for all the platforms, or not include any headers. For example, if a distribution build for powerpc includes the clang-resource-headers target, it will include all the x86 specific headers, even-though the x86 specific headers cannot be used.

This patch breaks up the clang-resource-headers list to a core list and platform specific lists. With the patch, a distribution build can now include the ppc-resource-headers to include the headers applicable to the powerpc platform.

Specifically, one can now have

cmake ... LLVM_DISTRIBUTION_COMPONENTS="clang;ppc-resource-headers" ... ../llvm
ninja install-distribution then installs the powerpc headers.

Similarly, one can do

cmake ... LLVM_DISTRIBUTION_COMPONENTS="clang;x86-resource-headers" ... ../llvm
to include headers applicable to the x86 platform in a distribution installation.

To implement this behaviour, the patch does two things

It breaks up the long files header file list to a core list and platform specific lists.
It adds numerous platform specific installation targets.

Differential Revision: https://reviews.llvm.org/D123498

Author: Qiongsi Wu