Hey Benny!

 BP> ncurses 6.5 is hardmasked in gentoo currently

Probably won't matter much now that you've traced it.  Having said that, I prefer to stay current as possible.

 BP> so lets solve fmail without break gentoo :)

It compiles fine here without any jiggery-pokery so it is in your capable hands now that you know the real issue.  And yes I used the latest setup here with gcc-4.1.0/glibc-2.40 to test the compile.

Life is good,
Maurice

 o-   o-  -o   -o   -o   -o   -o   -o    o-   o-   o-  -o    o-  -o    o-   o-
/)   /)    (\   (\   (\   (\   (\   (\  /)   /)   /)    (\  /)    (\  /)   /)
^^   ^^    ^^   ^^   ^^   ^^   ^^   ^^  ^^   ^^   ^^    ^^  ^^    ^^  ^^   ^^
... Hw‘r cwom mearg? Hw‘r cwom mago? Hw‘r cwom ma¨¨umgyfa?
    Where is now the horse? Where the young prince? Where the treasure-giver?
--- GNU bash, version 5.2.26(1)-release (x86_64-pc-linux-gnu)