Revert "Always compile with C99 standard."

This reverts commit d8145d79.

Makefile

@@ -39,7 +39,7 @@ CC:=$(shell sh -c 'type $(CC) >/dev/null 2>/dev/null && echo $(CC) || echo gcc')
 OPTIMIZATION?=-O3
 WARNINGS=-Wall -W -Wstrict-prototypes -Wwrite-strings
 DEBUG?= -g -ggdb
-REAL_CFLAGS=$(OPTIMIZATION) -fPIC -std=c99 -pedantic $(CFLAGS) $(WARNINGS) $(DEBUG) $(ARCH)
+REAL_CFLAGS=$(OPTIMIZATION) -fPIC $(CFLAGS) $(WARNINGS) $(DEBUG) $(ARCH)
 REAL_LDFLAGS=$(LDFLAGS) $(ARCH)
 
 DYLIBSUFFIX=so
@@ -133,7 +133,7 @@ check: hiredis-test
 	kill `cat /tmp/hiredis-test-redis.pid`
 
 .c.o:
-	$(CC) -c $(REAL_CFLAGS) $<
+	$(CC) -std=c99 -pedantic -c $(REAL_CFLAGS) $<
 
 clean:
 	rm -rf $(DYLIBNAME) $(STLIBNAME) $(TESTS) $(PKGCONFNAME) examples/hiredis-example* *.o *.gcda *.gcno *.gcov