[X86] Use single add/sub for large stack offsets

[X86] Use single add/sub for large stack offsets

For large stack offsets the compiler generates multiple immediate mode
sub/add instructions in the prologue/epilogue.  This patch makes the
compiler place the final amount to be added/subtracted into a register,
which is then added/substracted with a single operation.

Differential Revision: http://reviews.llvm.org/D7226

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227458 91177308-0d34-0410-b5e6-96231b3b80d8