[frontend] Add support for disabling the "inline" keyword using

-fno-inline-functions.

This behaves much like -fno-inline in gcc, but based on a discussion with 
Daniel it was decided that -fno-inline-functions should subsume -fno-inline.
Please speak up if you object.  The -fno-inline flag remains ignored.
Final part of rdar://10972766

llvm-svn: 152754