[cmake-developers] Implicit library trouble with mixed languages

[Christian Pfeiffer]

Hi folks,

I've tried to link some code built with GNU G++ together with the PGI 
Fortran compiler as linker. However, G++ pulls in libstdc++, which in 
turn depends on libgcc_s. Any library starting with 'gcc' is being 
ignored in CMakeParseImplicitLinkInfo.cmake L.136, so libgcc_s is being 
stripped from the commandline. PGI Fortran however does not need 
libgcc_s on its own and therefore won't link it. Alas, by stripping 
libgcc_s from the implicit library list, the linking process fails due 
to missing symbols. On a side note, PGI C also doesn't use libgcc_s, 
only PGI C++ does. In fact, using an all PGI environment yields the same 
issue.

I'd like to open an MR for this issue, but I'm not quite sure how to 
perform the cleanup as it exists right now in a fashion that doesn't 
include too many language-specific items on the link line - the reason 
this removal process exists - but yet works in a robust fashion. 
Ideally, we'd compare all enabled languages and strip the libraries that 
are being linked by all, but given the way that enable_language() can be 
called anywhere, that doesn't seem to lead to a solution to me.

Any suggestions on how to handle/fix the issue?

- Chris