Fix PR10884.

Fix PR10884.

This PR basically reports a problem where a crash in generated code
happened due to %rbp being clobbered:

  pushq %rbp
  movq  %rsp, %rbp
  ....
  vmovmskps %ymm12, %ebp
  ....
  movq  %rbp, %rsp
  popq  %rbp
  ret

Since Eric's r123367 commit, the default stack alignment for x86 32-bit
has changed to be 16-bytes. Since then, the MaxStackAlignmentHeuristicPass
hasn't been really used, but with AVX it becomes useful again, since per
ABI compliance we don't always align the stack to 256-bit, but only when
there are 256-bit incoming arguments.

ReserveFP was only used by this pass, but there's no RA target hook that
uses getReserveFP() to check for the presence of FP (since nothing was
triggering the pass to run, the uses of getReserveFP() were removed
through time without being noticed). Change this pass to use
setForceFramePointer, which is properly called by MachineFunction
hasFP method.

The testcase is very big and dependent on RA, not sure if it's worth
adding to test/CodeGen/X86.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139939 91177308-0d34-0410-b5e6-96231b3b80d8