longlong.h on mips with clang

* mpi/longlong.h [__mips__]: Use C-language version with clang.
--
clang doesn't recognise =l / =h assembly operand specifiers but apparently
handles C version well.

[jk: add changelog, rebase on libgcrypt repository, reformat changed line so it
 does not go over 80 characters]
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>

mpi/longlong.h

@@ -749,7 +749,8 @@ extern USItype __udiv_qrnnd ();
  **************  MIPS  *****************
  ***************************************/
 #if defined (__mips__) && W_TYPE_SIZE == 32
-#if (__GNUC__ >= 5) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4)
+#if defined (__clang__) || (__GNUC__ >= 5) || (__GNUC__ == 4 && \
+                                               __GNUC_MINOR__ >= 4)
 #define umul_ppmm(w1, w0, u, v) \
   do {                                                                  \
     UDItype _r;                                                         \