This fixes PR22248 on s390x. The previous attempt at this was D19101,
which was before LOAD_STACK_GUARD existed. Compared to the previous
version, this always emits a rather ugly block of 4 instructions, involving
a thread pointer load that can't be shared with other potential users.
However, this is necessary for SSP - spilling the guard value (or thread
pointer used to load it) is counter to the goal, since it could be
overwritten along with the frame it protects.
Differential Revision: http://reviews.llvm.org/D19363
llvm-svn: 267340
Matt Arsenault