make: Avoid stdout for compiler tests

Compiling to stdout fails at least with gcc 12 on Linux. Compile
directly to /dev/null instead.

GNUmakefile

@@ -24,10 +24,12 @@ NODIST=			poser/zimk
 
 HAVE_KQUEUE=		$(shell echo '#include <sys/event.h>\n'\
 			'int (*f)(void) = kqueue;' | \
-			$(or $(CC),cc) -xc -c -o- - >/dev/null 2>&1 && echo 1)
+			$(or $(CC),cc) -xc -c -o/dev/null - 2>/dev/null \
+			&& echo 1)
 HAVE_INOTIFY=		$(shell echo '#include <sys/inotify.h>\n'\
 			'int (*f)(void) = inotify_init;' | \
-			$(or $(CC),cc) -xc -c -o- - >/dev/null 2>&1 && echo 1)
+			$(or $(CC),cc) -xc -c -o/dev/null - 2>/dev/null \
+			&& echo 1)
 BOOLCONFVARS_OFF+=	$(if $(HAVE_KQUEUE),,WITH_KQUEUE) \
 			$(if $(HAVE_INOTIFY),,WITH_INOTIFY)
 BOOLCONFVARS_ON+=	$(if $(HAVE_KQUEUE),WITH_KQUEUE,) \