Remove all knowledge of UINT_TO_FP from the X86 backend, relying on the

Remove all knowledge of UINT_TO_FP from the X86 backend, relying on the
legalizer to eliminate them.  With this comes the expected code quality
improvements, such as, for this:

double foo(unsigned short X) { return X; }

we now generate this:

_foo:
        subl $4, %esp
        movzwl 8(%esp), %eax
        movl %eax, (%esp)
        fildl (%esp)
        addl $4, %esp
        ret

instead of this:

_foo:
        subl $4, %esp
        movw 8(%esp), %ax
        movzwl %ax, %eax   ;; Load not folded into this.
        movl %eax, (%esp)
        fildl (%esp)
        addl $4, %esp
        ret

-Chris

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22449 91177308-0d34-0410-b5e6-96231b3b80d8