When building for a mingw target, HAVE_GETTIMEOFDAY is defined (as the gettimeofday function was found), but the #ifdef _WIN32 #else block never tried to include <sys/time.h> (which provides the declaration) and/or <time.h> for such targets. This caused gettimeofday to be used without a prior declaration.
This has been visible as an easily overlooked warning, but Clang 15 changed this into a fatal error by default, when building in C99 mode (or newer).  (While Clang 15 still is under development, this may still change before it's released, but the warning is valid in any case.)
Decouple including of those headers from the #ifdef _WIN32 #else block and just check their corresponding availability defines.
This fixes issue #8.