longlong.h: Disable alpha umul_ppmm for old g++

Causes "unexpected AST of kind MULT_HIGHPART" error with
bootstrap from gcc 4.8.

        * longlong.h [__alpha] (umul_ppmm): Disable for c++.

From-SVN: r216811

include/ChangeLog

+2014-10-28  Richard Henderson  <rth@redhat.com>
+
+	* longlong.h [__alpha] (umul_ppmm): Disable for c++.
+
 2014-10-28  Yury Gribov  <y.gribov@samsung.com>
 
 	* libiberty.h (strtol, strtoul, strtoll, strtoull): New prototypes.

include/longlong.h

@@ -139,6 +139,9 @@ extern const UQItype __clz_tab[256] attribute_hidden;
 #endif /* __aarch64__ */
 
 #if defined (__alpha) && W_TYPE_SIZE == 64
+/* There is a bug in g++ before version 5 that
+   errors on __builtin_alpha_umulh.  */
+#if !defined(__cplusplus) || __GNUC__ >= 5
 #define umul_ppmm(ph, pl, m0, m1) \
   do {									\
     UDItype __m0 = (m0), __m1 = (m1);					\
@@ -146,6 +149,7 @@ extern const UQItype __clz_tab[256] attribute_hidden;
     (pl) = __m0 * __m1;							\
   } while (0)
 #define UMUL_TIME 46
+#endif /* !c++ */
 #ifndef LONGLONG_STANDALONE
 #define udiv_qrnnd(q, r, n1, n0, d) \
   do { UDItype __r;							\