[SAOC 25] improve importC weekly update 17

[Emmanuel]

Hi all,


This week I was able to fix building static library with importC 
on static functions.
see issue : https://github.com/dlang/dmd/issues/22153.

in my investigations, I realized when static function 
redeclarations are encountered where the later one is a 
definition, the replacement does wasn't reflecting in backend. so 
the backend was always picking the function with no body. I had 
to transfer the functions definitions to the declarations for 
functions that needed internal linkage and resolutions.
and that fixed it.

see PR: 
https://github.com/dlang/dmd/pull/22360#pullrequestreview-3642954373


I tested with several libraries compiling them `-lib`. I also 
caught an extra issue that needed fixing. I realized that when 
the static function is referenced globally by its address, it is 
still not resolved in backend, but when it is referenced by its 
address locally, it works fine. this was caught when testing zlib 
library that use const initializers to reference functions.

see issue: https://github.com/dlang/dmd/issues/22365.
looking through it and I hope I get it fixed soon.