php: fix build with mysqli

This fixes autobuild failures like
http://autobuild.buildroot.net/results/3288b742cee650ee47a41c5b4d6aaef1fe67bff1



php compile breaks with:

ext/mysqlnd/mysqlnd_auth.o: In function `php_mysqlnd_scramble_sha2':
mysqlnd_auth.c:(.text+0x1054): undefined reference to `PHP_SHA256Init'
mysqlnd_auth.c:(.text+0x1064): undefined reference to `PHP_SHA256Update'
mysqlnd_auth.c:(.text+0x1070): undefined reference to `PHP_SHA256Final'
mysqlnd_auth.c:(.text+0x1078): undefined reference to `PHP_SHA256Init'
mysqlnd_auth.c:(.text+0x1088): undefined reference to `PHP_SHA256Update'
mysqlnd_auth.c:(.text+0x1094): undefined reference to `PHP_SHA256Final'
mysqlnd_auth.c:(.text+0x109c): undefined reference to `PHP_SHA256Init'
mysqlnd_auth.c:(.text+0x10ac): undefined reference to `PHP_SHA256Update'
mysqlnd_auth.c:(.text+0x10bc): undefined reference to `PHP_SHA256Update'
mysqlnd_auth.c:(.text+0x10c8): undefined reference to `PHP_SHA256Final'

It looks like the php mysqli extension needs the hash extension to work.  This
seems to be a php Make dependany bug.  This patch works around it until the
upstream maintainers can fix it.

Signed-off-by: Christopher McCrory <chrismcc@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>