Mark ARM eh_sjlj_dispatchsetup as clobbering all registers. Radar 10567930.

We used to rely on the *eh_sjlj_setjmp instructions to mark that a function
with setjmp/longjmp exception handling clobbers all the registers.  But with
the recent reorganization of ARM EH, those eh_sjlj_setjmp instructions are
expanded away earlier, before PEI can see them to determine what registers to
save and restore.  Mark the dispatchsetup instruction in the same way, since
that instruction cannot be expanded early.  This also more accurately reflects
when the registers are clobbered.

llvm-svn: 146949