shadowsocks-libev: add dependency on sync builtins

libcork (bundled inside shadowsocks-libev) uses the __sync builtins
for atomic operations: the 4-byte variant on 32 bits platforms and the
8-byte variant on 64-bits platform.

Fixes:

  http://autobuild.buildroot.net/results/552b09ffe951c429422529c895f4c3ec723cf5ab

Signed-off-by: Min Xu <xuminready@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/shadowsocks-libev/Config.in

@@ -1,5 +1,7 @@
 config BR2_PACKAGE_SHADOWSOCKS_LIBEV
 	bool "shadowsocks-libev"
+	depends on BR2_TOOLCHAIN_HAS_SYNC_4 # for libcork
+	depends on BR2_TOOLCHAIN_HAS_SYNC_8 || !BR2_ARCH_IS_64 # for libcork
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_C_ARES
@@ -14,5 +16,7 @@ config BR2_PACKAGE_SHADOWSOCKS_LIBEV
 	  https://github.com/shadowsocks/shadowsocks-libev
 
 comment "shadowsocks-libev needs a toolchain w/ threads"
+	depends on BR2_TOOLCHAIN_HAS_SYNC_4
+	depends on BR2_TOOLCHAIN_HAS_SYNC_8 || !BR2_ARCH_IS_64
 	depends on BR2_USE_MMU
 	depends on !BR2_TOOLCHAIN_HAS_THREADS