Merging r261039:

Merging r261039:
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r261039 | rnk | 2016-02-16 16:17:33 -0800 (Tue, 16 Feb 2016) | 6 lines

[X86] Fix a shrink-wrapping miscompile around __chkstk

__chkstk clobbers EAX. If EAX is live across the prologue, then we have
to take extra steps to save it. We already had code to do this if EAX
was a register parameter. This change adapts it to work when shrink
wrapping is used.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@261136 91177308-0d34-0410-b5e6-96231b3b80d8