Pull in r175962 from upstream llvm trunk:
Pull in r175962 from upstream llvm trunk:

  X86: Disable cmov-memory patterns on subtargets without cmov.

  Fixes PR15115.

For the i386 arch, this should enable cmov instructions only on
-march=pentiumpro and higher.  Since our default CPU is i486, cmov
instructions will now be disabled by default.

MFC after:	1 week

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