jq: Set -std=c99 CLFAGS

Fixes build errors/warnings:

locfile.c: In function 'locfile_init':
locfile.c:21:3: error: 'for' loop initial declarations are only allowed
in C99 mode
   for (int i=0; i<length; i++) {

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

utils/jq/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=jq
 PKG_VERSION:=1.5
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_LICENSE:=BSD
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
@@ -24,6 +24,8 @@ ifdef CONFIG_USE_MIPS16
   TARGET_CFLAGS += -fno-ipa-sra
 endif
 
+TARGET_CFLAGS += -std=c99
+
 define Package/jq
   SECTION:=utils
   CATEGORY:=Utilities