Mark the Int_eh_sjlj_dispatchsetup pseudo instruction as clobbering all

Mark the Int_eh_sjlj_dispatchsetup pseudo instruction as clobbering all
registers.  Previously, the register we being marked as implicitly defined, but
not killed.  In some cases this would cause the register scavenger to spill a
dead register.

Also, use an empty register mask to simplify the logic and to reduce the memory
footprint.
rdar://12592448

llvm-svn: 167499