mksysinfo: change test == to test =

Fixes https://gcc.gnu.org/PR91621

Change-Id: I8289fab15506d25d014b07a4cb62b49dde38d79a
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/194569
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/libgo/mksysinfo.sh b/libgo/mksysinfo.sh
index 5f7b5f0..d616bd8 100755
--- a/libgo/mksysinfo.sh
+++ b/libgo/mksysinfo.sh
@@ -1123,7 +1123,7 @@
 # Prefer largefile variant if available.
 # CentOS 5 does not have f_flags, so pull from f_spare.
 statfs=`grep '^type _statfs64 ' gen-sysinfo.go || true`
-if test "$statfs" == ""; then
+if test "$statfs" = ""; then
   statfs=`grep '^type _statfs ' gen-sysinfo.go || true`
 fi
 if ! echo "$statfs" | grep f_flags; then