Fold subtracts into integer compares vs. zero. This improves generate code for this...

Fold subtracts into integer compares vs. zero. This improves generate code for this case on X86
from
_foo:
        movl    $99, %ecx
        movl    4(%esp), %eax
        subl    %eax, %ecx
        xorl    %edx, %edx
        testl   %ecx, %ecx
        cmovs   %edx, %eax
        ret

to
_foo:
        xorl    %ecx, %ecx
        movl    4(%esp), %eax
        cmpl    $99, %eax
        cmovg   %ecx, %eax
        ret

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45173 91177308-0d34-0410-b5e6-96231b3b80d8