libgo: use SYS_timer_settime32

Musl defines SYS_timer_settime32, not SYS_timer_settime, on 32-bit systems.

Based on patch by Sören Tempel.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/420222

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-a62f20ae78ddd41be682dde8cab075ca4f5dbb2a
+d53e8a0e94e34dc609e34dd5e404debda2640cfb
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/sysinfo.c

@@ -354,6 +354,11 @@ enum {
 };
 #endif
 
+#if !defined(SYS_timer_settime) && defined(SYS_timer_settime32)
+// musl defines SYS_timer_settim32 on 32-bit systems.
+#define SYS_timer_settime SYS_timer_settime32
+#endif
+
 #if defined(HAVE_LOFF_T)
 // loff_t can be defined as a macro; for -fgo-dump-spec make sure we
 // see a typedef.