Fix sign extend to long. When coming from sbyte, we used to generate:

        movsbl 4(%esp), %eax
        movl %eax, %edx
        sarl $7, %edx

Now we generate:

        movsbl 4(%esp), %eax
        movl %eax, %edx
        sarl $31, %edx

Which is right.

llvm-svn: 19515