[SAOC 25] improve importC weekly update 15

[Emmanuel]

Hi all,

this week I worked on getting `__FUNCTION__` and 
`__PRETTY_FUNCTION__` macro being known in importC. I discovered 
it being an error when compiling s7 library.

Link to PR: 
https://github.com/dlang/dmd/pull/22241#event-21731520913


I have been able to successfully convert the importC usage of 
complex library to the fundamental type and and now s7 library 
compiles. all the issues I reported have been fixed.
importC users can now compile s7 library.

link to PR: https://github.com/dlang/dmd/pull/22238