powerpc/math-emu: Update macros from GCC

powerpc/math-emu: Update macros from GCC

The add_ssaaaa, sub_ddmmss, umul_ppmm and udiv_qrnnd macros originate
from GCC's longlong.h which in turn was copied from GMP's longlong.h a
few decades ago.

This was found when compiling with clang:

   arch/powerpc/math-emu/fnmsub.c:46:2: error: invalid use of a cast in a
   inline asm context requiring an l-value: remove the cast or build with
   -fheinous-gnu-extensions
           FP_ADD_D(R, T, B);
           ^~~~~~~~~~~~~~~~~
   ...

   ./arch/powerpc/include/asm/sfp-machine.h:283:27: note: expanded from
   macro 'sub_ddmmss'
                  : "=r" ((USItype)(sh)),                                  \
                          ~~~~~~~~~~^~~

Segher points out: this was fixed in GCC over 16 years ago
( https://gcc.gnu.org/r56600 ), and in GMP (where it comes from)
presumably before that.

Update the add_ssaaaa, sub_ddmmss, umul_ppmm and udiv_qrnnd macros to
the latest GCC version in order to git rid of the invalid casts. These
were taken as-is from GCC's longlong in order to make future syncs
obvious. Other parts of sfp-machine.h were left as-is as the file
contains more features than present in longlong.h.

Link: https://github.com/ClangBuiltLinux/linux/issues/260
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>