Move Compiler.h from Demangle back to Support

Code review feedback from r328123 prefers copying the few feature test
macros used by Demangle into there, rather than sinking the header into
an odd corner like Demangle.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333965 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed