php: add missing select BR2_PACKAGE_LIBMCRYPT

Fixes:

  http://autobuild.buildroot.org/results/b0c/b0c9ea0d577a74549476ddbdb0d2ecd09311c765/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/php/Config.ext

@@ -67,6 +67,7 @@ config BR2_PACKAGE_PHP_EXT_HASH
 
 config BR2_PACKAGE_PHP_EXT_MCRYPT
 	bool "mcrypt"
+	select BR2_PACKAGE_LIBMCRYPT
 	help
 	  mcrypt support