[x86][inline-asm][clang] accept 'v' constraint

Commit in the name of: Coby Tayree 

1.'v' constraint for (x86) non-avx arch imitates the already implemented 'x' constraint, i.e. allows XMM{0-15} & YMM{0-15} depending on the apparent arch & mode (32/64).
2.for the avx512 arch it allows [X,Y,Z]MM{0-31} (mode dependent)

This patch applies the needed changes to clang
 LLVM patch: https://reviews.llvm.org/D25005

Differential Revision: D25004 

llvm-svn: 283716