Fix #75871 - If pkg-config is available use it for libxml2

[pmmaga]

Link for bugsnet: https://bugs.php.net/bug.php?id=75871

This removes the dependency on xml2-config but keeps it as a fallback in case pkg-config is not available.

[Majkl578]

[Bug report author here] I can confirm this works with both the new version without xml2-config and the previous one with it. 👍

[weltling]

Thanks for the PR. Perhaps it would be more correct to keep xml2-config as default. I was just comparing the outputs, fe on OpenSUSE i see

$ xml2-config --libs
-lxml2 -L/lib64 -lz -llzma -lm -ldl
$ pkg-config --libs libxml-2.0
-lxml2

Given that's only Debian for now, and only experimental, seems the other way round, to keep xml2-config and fallback to pkg-config, would be more backward compatible.

Thanks.

[pmmaga]

Thanks for the feedback! I've switched the precedence so xml2-config is still used when present.

[pmmaga]

Reverted trailing white-space changes

[weltling]

@pmmaga one question yet - any particular reason to target 7.1? Experimental might land or not, actually. If it went into unstable, we could put it, but otherwise master seems a good target for us. What would you say?

Thanks.

[pmmaga]

As it was a bug report I just followed the standard: "lowest actively supported branch that is affected". Given the way it is now implemented, nothing will change for people that have xml2-config available, so I'd say it's safe to support this from 7.1+. If anyway you'd prefer to see this only on master I also understand the reasoning, so both ways are fine for me.

[krakjoe]

@weltling I think I'm happy to merge into 7.1 if the default behaviour is retained, okay ?

[weltling]

@krakjoe ack, please do. Of course, one can see it separate from the Debian experimental.

Thanks.

[krakjoe]

Merged 5673c64

Thanks.