Now that the lowerinvoke pass inserts calls to llvm.setjmp/llvm.longjmp, some

hacks can be banished.  Also, this gives us the opportunity to emit special code
for the setjmp/longjmps which alows the elimination of one GCC warning for every
setjmp/longjmp site (which is often THOUSANDS in C++ programs).  Yaay!

llvm-svn: 11484