mips: fix pipe syscall decoding

* linux/mips/arch_getrval2.c: New file.
* Makefile.am (EXTRA_DIST): Add it.
* defs.h [MIPS] (HAVE_GETRVAL2): Define.
diff --git a/defs.h b/defs.h
index 5d2a76e..6e43682 100644
--- a/defs.h
+++ b/defs.h
@@ -425,7 +425,8 @@
 extern int umovestr(struct tcb *, long, unsigned int, char *);
 extern int upeek(int pid, long, long *);
 
-#if defined ALPHA || defined IA64 || defined SH || defined SPARC || defined SPARC64
+#if defined ALPHA || defined IA64 || defined MIPS \
+ || defined SH || defined SPARC || defined SPARC64
 # define HAVE_GETRVAL2
 extern long getrval2(struct tcb *);
 #else