PE/COFF: add ARM NT reference kinds

Teach the reader about ARM NT relocation types.  Although the writer cannot yet
perform the actual application of these relocations, the reader can at least now
identify the relocation types.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@219178 91177308-0d34-0410-b5e6-96231b3b80d8
PE/COFF: rename applyRelocations* family

Use x86 and x64 which is the canonical Microsoft vernacular for the targets.
Addresses post-commit review comments from Rui.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@219179 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Infer machine type from input object file

If /machine option is omitted, the linker needs to infer that from
input object files. This patch implements that.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@219180 91177308-0d34-0410-b5e6-96231b3b80d8