re PR go/81893 (compilation error in libgo starting with r251127)

	PR go/81893
    runtime: only use PPC GNU/Linux register code on little endian
    
    Reportedly the current code builds on little endian but not big endian.
    
    Fixes https://gcc.gnu.org/PR81893.
    
    Reviewed-on: https://go-review.googlesource.com/57110

From-SVN: r251188

gcc/go/gofrontend/MERGE

-28e49825162465172ed706283628bf5cc1996260
+2c4a2bd826e58c8c8c51b9196c8d2c67abc4037e
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/go-signal.c

@@ -343,7 +343,7 @@ dumpregs(siginfo_t *info __attribute__((unused)), void *context __attribute__((u
   #endif
 #endif
 
-#ifdef __PPC__
+#if defined(__PPC__) && defined(__LITTLE_ENDIAN__)
   #ifdef __linux__
 	  {
 		mcontext_t *m = &((ucontext_t*)(context))->uc_mcontext;
@@ -359,6 +359,9 @@ dumpregs(siginfo_t *info __attribute__((unused)), void *context __attribute__((u
 		runtime_printf("xer %X\n", m->regs->xer);
 	  }
   #endif
+#endif
+
+#ifdef __PPC__
   #ifdef _AIX
 	  {
 		mcontext_t *m = &((ucontext_t*)(context))->uc_mcontext;