Avoid a fall-through in the (stubby) treatment of the longjmp intrinsic
call which causes llc & lli to core-dump.

Add a sort-of treatment of cast double to ulong. I am not really sure
what a user should expect to see upon casting a negative FP value to
unsigned long long. But with what is given here, I was able to write
a program that could cast -123.456 to ulong and back and get -123.0,
which seems like a step in the right direction.  GCC seems to give you
0. I don't know if I'd consider that useful.

These cases were coming up in GNU coreutils-5.0.

llvm-svn: 7205