Summary: Currently there is no way to disable deprecated warning from asm like this

clang  -target arm deprecated-asm.s -c
  deprecated-asm.s:30:9: warning: use of SP or PC in the list is deprecated
       stmia   r4!, {r12-r14}

We have to have an option what can disable it.

Patched by Yin Ma!

Reviewers: joey, echristo, weimingz

Subscribers: llvm-commits, aemerson

Differential Revision: https://reviews.llvm.org/D27219

llvm-svn: 288734