Configure: check usability of <stdckdint.h>, not only its existence

[t-a-k]

Some FreeBSD systems have <stdckdint.h>, but it cannot be compiled with C++ compilers. This patch modifies Configure to check whether ckd_* functions can be compiled, and leave I_STDCKDINT undefined (so that <stdckdint.h> won't be used in build time) if the compilation failed.

Will fix GH #23725.

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• This set of changes does not require a perldelta entry.

[jkeenan]

IIUC, the differences which your patch would effect could be detected simply by running ./Configure, i.e., even before running make.

I decided to use the same FreeBSD machine on which I explored #23725 to test this out. I took my regular configuration command (which by default uses clang in whatever is its current default version), substitute in clang++ (in its current default version, 18):

sh ./Configure -des -Dusedevel \
  -Dcc=clang++ \
  -Duseithreads \
  -Doptimize="-O2 -pipe -fstack-protector-strong -fno-strict-aliasing"

... and use that first on blead, then on the branch in your pull request. I then compared their respective config.sh files. This is what I got:

diff --ignore-matching-lines 'Configuration time:' \
     --ignore-matching-lines 'cf_time=' \
     blead.clang++.config.sh \
     branch.clang++.config.sh

814c814
< i_stdckdint='define'
---
> i_stdckdint='undef'

@t-a-k, is this what you would have expected?

On each of these two builds I then ran make test_prep. In blead, the build failed in the same way as reported in #23725 (comment). In branch, the build succeeded, as did make test_harness.

$ ./perl -Ilib -v | head -2 | tail -1
This is perl 5, version 43, subversion 3 (v5.43.3 (v5.43.2-339-g9f09ee5689)) built for amd64-freebsd-thread-multi

$ ./perl -Ilib -V:config_args
config_args='-des -Dusedevel -Dcc=clang++ -Duseithreads -Doptimize=-O2 -pipe -fstack-protector-strong -fno-strict-aliasing';

This pull request DWIMs for me, but it should also be reviewed by people more familiar with ./Configure than me. @khwilliamson, @Tux, can you take a look?

[t-a-k]

Thank you for testing!

... and use that first on blead, then on the branch in your pull request. I then compared their respective config.sh files. This is what I got:

diff --ignore-matching-lines 'Configuration time:' \
     --ignore-matching-lines 'cf_time=' \
     blead.clang++.config.sh \
     branch.clang++.config.sh

814c814
< i_stdckdint='define'
---
> i_stdckdint='undef'

@t-a-k, is this what you would have expected?

Yes. In this case <stdckdint.h> is present but fails to compile with specified compiler (probably because it is not compatible with C++), therefore Configure in this branch will set i_stdckdint to undef to indicate <stdckdint.h> is not usable.

[khwilliamson]

My question is, is there a C++ compatible hdr that would serve instead of this

[khwilliamson]

And the answer to my question is no