Fix s_lock_test compile

This is a mostly unused tool, but I discovered while nosing around the
Makefile that it hasn't been kept in line with other changes.  Fix it.

Backpatching doesn't appear to be necessary.

Discussion: https://postgr.es/m/202401241114.ied53jcich72@alvherre.pgsql

src/backend/storage/lmgr/Makefile

@@ -33,7 +33,7 @@ endif
 s_lock_test: s_lock.c $(top_builddir)/src/common/libpgcommon.a $(top_builddir)/src/port/libpgport.a
 	$(CC) $(CPPFLAGS) $(CFLAGS) -DS_LOCK_TEST=1 $(srcdir)/s_lock.c \
 		$(TASPATH) -L $(top_builddir)/src/common -lpgcommon \
-		-L $(top_builddir)/src/port -lpgport -o s_lock_test
+		-L $(top_builddir)/src/port -lpgport -lm -o s_lock_test
 
 # see notes in src/backend/parser/Makefile
 lwlocknames.c: lwlocknames.h

src/backend/storage/lmgr/s_lock.c

@@ -61,6 +61,14 @@
 #define MIN_DELAY_USEC		1000L
 #define MAX_DELAY_USEC		1000000L
 
+#ifdef S_LOCK_TEST
+/*
+ * These are needed by pgstat_report_wait_start in the standalone compile of
+ * s_lock_test.
+ */
+static uint32 local_my_wait_event_info;
+uint32	   *my_wait_event_info = &local_my_wait_event_info;
+#endif
 
 slock_t		dummy_spinlock;