Warn about invalid return statements by default.

This fixes <rdar://problem/6839489> 10A345: Clang does not warm about mismatched returns (void return from a bool function)
 
Will implement -Wreturn-type, -Wno-return-type in another commit.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70492 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed