Allow to pass custom CFLAGS and LDFLAGS to the compilation of builtin extension modules

[pablogsal]

This gives redistributors more control over the compilation flags of the extension modules. This allows among other things to pass custom RPATH/RUNPATH values that point to the correct PLATDIR

Check #131781 for the discussion and rationale of why we decided to allow this

Linked PRs

• gh-131842: Allow to pass custom CFLAGS and LDFLAGS to the compilation of builtin extension modules #131847

[ned-deily]

@erlend-aasland, isn't this already supported for individual modules with the *_CFLAGS and *_LIBS configure options? I don't know if we still have or did have a global options for all extension modules.

[erlend-aasland]

Yes, this is already supported (and mostly documented IIRC).

[pablogsal]

What we are missing is a global option for ALL extension modules. Also, LIBS != LDFLAGS

Additionally, the individual flags aren't available for all modules, just a select few.

[erlend-aasland]

Right, we do not have anything like that IIRC. Thanks for clarifying.

[pablogsal]

Small note x-posted from #131781 (comment):

I checked and @ned-deily was right: as confusing as it is the *_LIBS are treated as LDFLAGS but only apply to individual (and not all) extension modules. Also they are only available for a select collection of them.

The PR still applies as we are adding a global addition for all of them

[erlend-aasland]

Correct, configure is not consequent regarding LIBS and LDFLAGS. That's worth a cleanup.

[ned-deily]

as confusing as it is the *_LIBS are treated as LDFLAGS but only apply to individual (and not all) extension modules

One further point of confusion (to which I may have added in my comment above): AFAIK, the intent is that those *_CFLAGS and *_LIBS configure options are for each third-party library we use (not each extension module) and their values apply to every extension module that uses that library; there are some third-party libs that are linked to more than one stdlib extension module. If there are any third-party libs that aren't covered, that's a bug.