[tlbuild] Issues with msys2: failed to link with -lgs, _mkdir not declared, ...

[Akira Kakuto]

Dear Mojca,

> zziplib has seen substantial changes yesterday, but its make check
> fails even on the latest Mac.

Is it related with the following?

(1) topdir/README
(2) topdir/test/README
(3) topdir/test/test.zip

In the original sources, (1) and (2) are different.
README in (3) is the same as (2), but different from (1).

Best,
Akira