Description:
------------
When trying to build extension mysqlnd using 'phpize', the follow error keeps popping up:
    configure: error: Cannot find OpenSSL's <evp.h>

The cause of this is because after running the command 'phpize' the configure script has a variable (PHP_OPENSSL_DIR) that is not set "yes"


PHP_OPENSSL_DIR is never initialized. So, the following code found on line 4332 never gets executed

    if test "$PHP_OPENSSL" = "yes" && test -x "$PKG_CONFIG" && \
       $PKG_CONFIG --exists openssl; then
        ...
        # checks openssl version, and other stuff



Test script:
---------------
# download and extract latest PHP 7 code
compile PHP using the following
./configure --prefix=$HOME/php7
make
make install
cd $HOME/php7
ln -s bin/php-config php-config
ln -s bin/php php
ln -s bin/phpize phpize
cd the directory where PHP source code is
cd ext
cd mysqlnd
# rename the configXX.m4 file to config.m4
phpize
./configure --with-php-config=$HOME/php7/php-config
make

Expected result:
----------------
The extension should be compiled and a shared object should be built and moved to the extension directory

Actual result:
--------------
./configure returns an error