openbsd: ensure we link to the built libperl.a, not the system libperl.a

[tonycoz]

When building with gcc, lib/ExtUtils/t/Embed.t would link against the system libperl.a rather than the newly built libperl.a.

Due to the limited API used by the sample code this typically didn't crash, but some configuration changes could result in a crash or a link error.

For OpenBSD, change the link options to more closely match those used when building the perl executable, which results in linking against the correct library.

Fixes #22125

Also adds a test to ensure we are linking against the correct libperl.

Smoke reports from before a trivial rebase at https://perl.develop-help.com/?b=smoke-me%2Ftonyc%2F22125-openbsd-embed

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• This set of changes requires a perldelta entry, and it is included.

[jkeenan]

@tonycoz, thanks for continuing to investigate this. Could you rebase your smoke-me branch and push this new code to that branch? That way, @cjg-cguevara's smoker will pick up the branch.

@afresh1, can you take a look at this p.r.? Thanks.

[jkeenan]

@tonycoz: I fetched your p.r. and built a perl locally per the following:

$ uname -mrs
OpenBSD 6.9 amd64
$ gcc --version
gcc (GCC) 4.2.1 20070719 
$ gitcurr
gh-23265-tonycoz-22125-openbsd-embed-20250507
$ ./perl -Ilib -V:config_args
config_args='-des -Dusedevel -Dcc=gcc -Accflags=-DPERL_RC_STACK -DDEBUG_LEAKING_SCALARS';
$ ./perl -Ilib -v | head -2 | tail -1
This is perl 5, version 41, subversion 13 (v5.41.13 (v5.41.12-41-g060adda81e)) built for OpenBSD.amd64-openbsd

This configuration was the first one I discussed in #22125. All tests PASSed. So that's a very good sign. I will want to re-test this with clang10 and g++. However, as previously reported my OpenBSD-VM version is obsolete, so we'll need feedback from people who have more up-to-date versions of the platform and its C-compilers. Having your p.r. code in the smoke-me branch will be very helpful for this.

[tonycoz]

Having your p.r. code in the smoke-me branch will be very helpful for this.

I pushed it to the smoke-me, https://perl.develop-help.com/?b=smoke-me%2Ftonyc%2F22125-openbsd-embed we're just waiting for results now.

[jkeenan]

I've also gotten a PASS with the following configuration:

$ ./perl -Ilib -V:config_args
config_args='-des -Dusedevel -Dcc=clang -Accflags=-DPERL_RC_STACK -DDEBUG_LEAKING_SCALARS';

Am beginning a smoke-test run with my customary configurations. That will take several hours. Note that I haven't looked at the code changes at all -- only the test results.

[afresh1]

I should be able to run tests with this. Will have to remember which architectures I have that still use gcc :-)