libgo: define SO_RCVTIMEO on 32-bit GNU/Linux

Fixes golang/go#42872

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/273892

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-45461eeba1db1a3b4194dc8ecc331c0e92f5ad4c
+be1738f1fff0e817d921ed568791f9b0585a6982
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/mksysinfo.sh

@@ -194,6 +194,7 @@ fi
 
 # Networking constants.
 egrep '^const _(AF|ARPHRD|ETH|IN|SOCK|SOL|SO|IPPROTO|TCP|IP|IPV6)_' gen-sysinfo.go |
+  grep -v '_val =' |
   sed -e 's/^\(const \)_\([^= ]*\)\(.*\)$/\1\2 = _\2/' >> ${OUT}
 grep '^const _SOMAXCONN' gen-sysinfo.go |
   sed -e 's/^\(const \)_\(SOMAXCONN[^= ]*\)\(.*\)$/\1\2 = _\2/' \
@@ -213,6 +214,14 @@ for m in SOCK_CLOEXEC SOCK_NONBLOCK; do
   fi
 done
 
+# On 32-bit GNU/Linux the expression for SO_RCVTIMEO is too complicated
+# for -fdump-go-spec.
+if ! grep '^const SO_RCVTIMEO ' ${OUT} >/dev/null 2>&1; then
+  if grep '^const _SO_RCVTIMEO_val' ${OUT} >/dev/null 2>&1; then
+    echo 'const SO_RCVTIMEO = _SO_RCVTIMEO_val' >> ${OUT}
+  fi
+fi
+
 # The syscall package requires AF_LOCAL.
 if ! grep '^const AF_LOCAL ' ${OUT} >/dev/null 2>&1; then
   if grep '^const AF_UNIX ' ${OUT} >/dev/null 2>&1; then

libgo/sysinfo.c

@@ -337,6 +337,9 @@ enum {
 #ifdef BIOCVERSION
   BIOCVERSION_val = BIOCVERSION,
 #endif
+#ifdef SO_RCVTIMEO
+  SO_RCVTIMEO_val = SO_RCVTIMEO,
+#endif
 };
 
 // SIOCGIFMTU can't be added in the above enum as it might