According to
https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_FLAGS_INIT.html
the _INIT variables should be set in the toolchain file.

Right now, zlib is only built for Windows, but we may eventually
changed that, so don't hard-code `win32/Makefile.gcc`.

Make sure all the gory details are visible in CI logs.

For better error logs on CI.

This compile-time option is not about debug logging, but about
curl_easy_strerror().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1670

Punycode hooray!

Fixes Android build failure with NDK r25 beta4 because "vulkan_beta.h"
was not found.