Description:
------------
I've just tried to compile the current 5.5 branch from git. ext/json fails to build.

My test machine runs a Ubuntu 12.10 standard configuration.

Linux 3.5.0-19-generic (64bit)
GCC 4.7.2

Test script:
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./configure --prefix=/opt/php/php-5.5-dev --enable-cli --with-zlib --with-pear
make

Expected result:
----------------
A compiled version of PHP 5.5.

Actual result:
--------------
/home/rabus/php-src/ext/json/json.c: In function ‘json_escape_string’:
/home/rabus/php-src/ext/json/json.c:422:6: warning: unknown conversion type character ‘k’ in format [-Wformat]
/home/rabus/php-src/ext/json/json.c: In function ‘php_json_encode’:
/home/rabus/php-src/ext/json/json.c:630:6: warning: unknown conversion type character ‘k’ in format [-Wformat]
make: *** No rule to make target `/home/rabus/php-src/ext/json/utf8_to_utf16.c', needed by `ext/json/utf8_to_utf16.lo'.  Stop.