fix imap c-client headers leaking into configure

[edram]

What does this PR do?

c-client currently installs its private headers, including unix.h, into the global include directory. PHP's configure check then detects that private header and defines HAVE_UNIX_H, causing installed PHP development headers to include a file that is not shipped with the PHP SDK package. As a result, downstream extensions fail to compile when they include php.h.

This keeps c-client headers under include/c-client, the layout already expected by ext-imap, so they are no longer visible to unrelated PHP configure checks.

Verification

• Reproduced the downstream SDK failure with the unmodified package: https://github.com/edram/mise-php/actions/runs/33045639321/job/98428862980
• Built and packaged the same PHP 8.3 GNU/Laravel target successfully with this change: https://github.com/edram/mise-php/actions/runs/33048935705/job/98439439481
• Installed and loaded asgrim/example-pie-extension through PIE, including phpize, configure, build, and install
• Built, installed, and loaded ds-1.8.0 through PECL
• Built PHP 8.3 with IMAP locally and verified the resulting CLI loads IMAP

Checklist before merging

• If you modified *.php or *.yml, run them locally to ensure your changes are valid:
  • composer cs-fix
  • composer analyse
  • composer test
  • bin/spc dev:lint-config

[henderkes]

Doesn't the extension need to be pointed at that dir then?

[edram]

Doesn't the extension need to be pointed at that dir then?

Good question. The extension does need to include that directory, but no
additional configure argument is required because --with-imap=DIR
expects the c-client installation prefix, not the header directory itself.

StaticPHP already passes:

--with-imap=<buildroot>

The upstream pecl-mail-imap config.m4 explicitly probes
$PHP_IMAP/include/c-client via IMAP_INC_CHK(/include/c-client).
Once found, it assigns that path to IMAP_INC_DIR and adds it with
PHP_ADD_INCLUDE($IMAP_INC_DIR):

https://github.com/php/pecl-mail-imap/blob/1.0.3/config.m4#L126-L139

I also verified that the generated PHP Makefile contains:

-I<buildroot>/include/c-client

and the resulting PHP binary builds and loads the imap extension
successfully. Passing <buildroot>/include/c-client directly to
--with-imap would be incorrect because the same prefix is also used to
locate <buildroot>/lib/libc-client.a.

[github-actions]

StaticPHP Test Bot

Detected: Extensions: none | Libraries: imap | Targets: none
Active labels: test/php-83
Available labels: need-test (gate), test/linux test/windows test/macos (platform), test/tier2 (extra arch), test/php-83 test/php-84 (PHP version), sapi/frankenphp (extra FrankenPHP SAPI build)
Config: Linux x86_64 + Windows x86_64 + macOS arm64 | PHP 8.3, PHP 8.5 NTS