[Bug #77241] ext/intl: Use pkg-config to detect icu

[hughmcmaster]

icu-config has been deprecated by its upstream developers for some years now. In icu 63.1, icu-config is optional to install, but is installed by default. In the next version, icu-config will no longer be installed by default.

The developers recommend downstream packages use pkg-config to detect the icu libraries.

Debian (and its derivatives, such as Ubuntu) will remove icu-config from its icu development package (libicu-dev) very soon. Hence, php needs to use pkg-config to detect icu.

[cmb69]

Closely related to PR #3654.

[hughmcmaster]

@nikic I've updated #3701. Thanks for the review.

[nikic]

LGTM. Only thing I'm uncertain about is whether we need to preserve the PHP_SETUP_ICU macro, so this is also usable by 3rd-party extension. I don't know if anything actually uses it, but it might be safer to keep it.

[hughmcmaster]

@nikic Thanks. Remember, though, that icu-config is deprecated and will be removed from icu in version 64. This means the PHP_SETUP_ICU macro will be redundant. Even now, it has a very limited lifespan.

That said, if you still want to keep the macro, I'll update the PR for this. Please let me know what you want to do.

[nikic]

@hughdavenport Yeah, we shouldn't keep the current implementation of the macro around, but it would be possible to move the new implementation into PHP_SETUP_ICU and then call PHP_SETUP_ICU from ext/intl, the way it was done previously.

[hughmcmaster]

@nikic That seems fair. I thought moving to ext/intl was a better option, because ext/gd does this for FreeType 2. Plus icu is used in ext/intl, so it has a closer relationship.

[hughmcmaster]

@nikic I've updated #3701 as discussed.

[nikic]

Merged as 20fa2e7. Thanks a lot!