FastISel can only append to basic blocks.
Compute the insertion point from the end of the basic block instead of
skipping labels from the front.
This caused failures in landing pads when live-in copies where inserted
before instruction selection.
I missed this change in r252720; without it, certain compilation flags
can cause exception labels to not be generated, but still referenced,
leading to link errors.
Reported by: zeising
MFC after: 3 days
7a06320990