[X86] Don't alter HasOpaqueSPAdjustment after we've relied on it
We rely on HasOpaqueSPAdjustment not changing after we've calculated
things based on it. Things like whether or not we can use 'rep;movs' to
copy bytes around, that sort of thing. If it changes, invariants in the
backend will quietly break. This situation arose when we had a call to
memcpy *and* a COPY of the FLAGS register where we would attempt to
reference local variables using %esi, a register that was clobbered by
the 'rep;movs'.
This fixes PR26124.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257730
91177308-0d34-0410-b5e6-
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