Hello, the issue with a debian package reported here also affects this Arch Linux package that was just updated to version 1.6.5. Since the latter package is installing libtcod by help of
make install without doing anything Arch-specific (see the PKGBUILD) it looks to me like this may not be a platform-dependent problem but an issue on your end.
The fix proposed for the Debian package also works under Arch: Replace
#include "external/pstdint.h" with