Attr: Remove ForceInline

The __forceinline keyword's semantics are now recast as AlwaysInline and
the kw___forceinline token has its language mode set for KEYMS.

This preserves the semantics of the previous implementation but with
less duplication of code.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202131 91177308-0d34-0410-b5e6-96231b3b80d8