Add Sema support for __builtin_setjmp/__builtin_longjmp. The primary

Add Sema support for __builtin_setjmp/__builtin_longjmp.  The primary
reason for adding these is to error out in CodeGen when trying to generate
them instead of silently emitting a call to a non-existent function.

(Note that it is not valid to lower these to setjmp/longjmp; in addition
to that lowering being different from the intent, setjmp and longjmp
require a larger buffer.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70658 91177308-0d34-0410-b5e6-96231b3b80d8