Implement EmitUsualArithmeticConversions, so we can add shorts to floats and

ints to long long etc.  For int to longlong, we now get:

        %tmp = load i64* %F             ; <i64> [#uses=1]
        %tmp1 = load i32* %D            ; <i32> [#uses=1]
        %promote = sext i32 %tmp1 to i64                ; <i64> [#uses=1]
        %tmp2 = add i64 %tmp, %promote          ; <i64> [#uses=0]

llvm-svn: 39576