getRegClassForInlineAsmConstraint to being handled by
getRegForInlineAsmConstraint.  This allows us to let the llvm register allocator
allocate, which gives us better code.  For example, X86/2007-01-29-InlineAsm-ir.ll
used to compile to:

_run_init_process:
        subl $4, %esp
        movl %ebx, (%esp)
        xorl %ebx, %ebx
        movl $11, %eax
        movl %ebx, %ecx
        movl %ebx, %edx
        # InlineAsm Start
        push %ebx ; movl %ebx,%ebx ; int $0x80 ; pop %ebx
        # InlineAsm End

Now we get:
_run_init_process:
        xorl %ecx, %ecx
        movl $11, %eax
        movl %ecx, %edx
        # InlineAsm Start
        push %ebx ; movl %ecx,%ebx ; int $0x80 ; pop %ebx
        # InlineAsm End

llvm-svn: 35804