Undefined use of weak symbols in gnulib

[Paul Eggert]

On 7/27/21 1:19 PM, Florian Weimer wrote:
>> So if there's any change regarding LIBPTHREAD_SO, I think the natural one
>> would be to define it to LIBC_SO (I hope the dlopen/dlsym case works
>> regardless of whether that change is made or not).
> That is in an interesting idea.  I like it.

Me too.

> It doesn't help with Bruno's use case, detecting the integrated
> libpthread with the preprocessor.

It might be good enough for that use case, if the detection of 
LIBPTHREAD_SO==LIBC_SO can be done at 'configure' time instead of at 
preprocessor time. (Bruno would be a better person to opine on this.)