[bug#40164] Fix for libgccjit

[Formbi]

> I think this has no effect because this ‘native-search-paths’ is already
> inherited from ‘gcc-9’, which ‘libgccjit’ inherits from.

Nope, it does have an effect. I added "lib/gcc" to the original paths (and that 
was the needed thing).

(sending again because I forgot about the debbugs e-mail)