Revert "Attributes on K&R C functions should not cause incompatible..."

...function type with a redeclaration having the same attribute. Fixing this
introduced a secondary problem where we were assuming that K&R functions
could not be attributed types when reporting old-style function definitions
that are not preceded by a prototype."

Also Revert "Hopefully fixes a compile error introduced by r294861."

This reverts commit r294862, r294861, as they bork the ARM builds and
haven't fix it back.

Also, please, short commit titles, long commit decsriptions...

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@294910 91177308-0d34-0410-b5e6-96231b3b80d8