Ability to provide custom librdkafka path during install

[Wirone]

Solution taken from ssh2 extension, thanks to this I was able to install that extension with pecl install ssh2 and provide Homebrew's path to libssh2.

Tested by cloning this repo, checking out patch-1 branch and executing pecl install package.xml:

...
librdkafka installation path? [autodetect] : /opt/homebrew/opt/librdkafka
building in /private/tmp/pear/temp/pear-build-gkorbaaNXDnl/rdkafka-6.0.2
running: /private/tmp/pear/temp/rdkafka/configure --with-php-config=/opt/homebrew/opt/php@7.4/bin/php-config --with-rdkafka=/opt/homebrew/opt/librdkafka
...
Build process completed successfully
Installing '/Users/gkorba/.asdf/installs/php/7.4.30/lib/php/extensions/no-debug-non-zts-20190902/rdkafka.so'
install ok: channel://pecl.php.net/rdkafka-6.0.2
configuration option "php_ini" is not set to php.ini location
You should add "extension=rdkafka.so" to php.ini

It worked 🎉

Fixes #503

[Wirone]

FYI: on Homebrew's PHP it was failing with missing pcre2.h though. --with-pcre-regex / --with-pcre-dir (found here) and --with-external-pcre (found here) was not working (unrecognized option) 😩 I was able to workaround PCRE2 problem with:

ln -s /opt/homebrew/opt/pcre2/include/pcre2.h /opt/homebrew/Cellar/php@7.4/7.4.30/include/php/ext/pcre/pcre2.h

which is not proper solution, but it allowed me to test if extension is built and working.

On asdf's PHP (7.4, 8.1) extension was properly installed just by passing path to PCRE2. So it seems like it's working 🙂

[arnaud-lb]

Awesome! Thank you.

The interactive prompt doesn't appear to break non-interactive installs, so that's great.

[arnaud-lb]

Released on pecl in version 6.0.3