package/php: fix build without threads

Fix the following build failure without threads raised since bump to
version 8.3.4 in commit e50460f9f12a8c5f82f2166733afe9cca3c8cd19 and
https://github.com/php/php-src/commit/a11c8a30399e90c17c287b9656c0077bc5131c9c:

/home/buildroot/instance-0/output-1/build/php-8.3.4/Zend/zend_call_stack.c:39:11: fatal error: pthread.h: No such file or directory
   39 | # include <pthread.h>
      |           ^~~~~~~~~~~

Fixes: e50460f9f12a8c5f82f2166733afe9cca3c8cd19
 - http://autobuild.buildroot.org/results/a4ef648a9da50b26ed56d5d490e4cf5a1bfff970

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
1 file changed