package/php-apcu: fix build without __sync_*_4 intrinsics

Fix the following build failure raised since the addition of the package
in commit 8ddeeffa186d8bce875ac713c1e71483c618842a:

configure: error: Compiler does not support atomics

--enable-apcu-rwlocks can't be used until
https://github.com/krakjoe/apcu/pull/430 is merged (and autoreconf does
not work either)

Fixes:
 - http://autobuild.buildroot.org/results/efa/efa3b4406f87a1e9521b66f392a6fa19ac01f0cd/build-end.log

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/php-apcu/php-apcu.mk

@@ -22,4 +22,8 @@ define PHP_APCU_PHPIZE
 endef
 PHP_APCU_PRE_CONFIGURE_HOOKS += PHP_APCU_PHPIZE
 
+ifeq ($(BR2_TOOLCHAIN_HAS_SYNC_4),)
+PHP_APCU_CONF_OPTS += --disable-apcu-rwlocks
+endif
+
 $(eval $(autotools-package))