cjson: fix build for toolchains without ssp

Set ENABLE_CUSTOM_COMPILER_FLAGS to OFF to disable custom flags, in
particular -fstack-protector-strong which depends on
BR2_TOOLCHAIN_HAS_SSP

Fixes:

  http://autobuild.buildroot.net/results/cfcf3bc8066159dfddd1786954d78e8527858f2f/

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/cjson/cjson.mk

@@ -9,7 +9,10 @@ CJSON_SITE = $(call github,DaveGamble,cjson,$(CJSON_VERSION))
 CJSON_INSTALL_STAGING = YES
 CJSON_LICENSE = MIT
 CJSON_LICENSE_FILES = LICENSE
+# Set ENABLE_CUSTOM_COMPILER_FLAGS to OFF in particular to disable
+# -fstack-protector-strong which depends on BR2_TOOLCHAIN_HAS_SSP
 CJSON_CONF_OPTS += \
-	-DENABLE_CJSON_TEST=OFF
+	-DENABLE_CJSON_TEST=OFF \
+	-DENABLE_CUSTOM_COMPILER_FLAGS=OFF
 
 $(eval $(cmake-package))