[mips] Added support for assembling sdbbp.

Summary:
This instruction is re-encoded in MIPS32r6/MIPS64r6 without changing the
restrictions. We hadn't implemented it for earlier ISA's so it has been added to those too.

Differential Revision: http://reviews.llvm.org/D4265


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211590 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r211287, "Remove support for LLVM runtime multi-threading."

libclang still requires it on cygming, lack of incomplete <mutex>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211592 91177308-0d34-0410-b5e6-96231b3b80d8