Revert r304953 for release 5.0.0

This is causing failures when compiling clang with -O3
as one of the structures used by clang is passed by
value and uses the fastcc calling convention.

Faliures manifest for stage2 mips build.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@310057 91177308-0d34-0410-b5e6-96231b3b80d8