It is not only shorter than `not meson.is_cross_build() or
meson.has_exe_wrapper()` but also handle the case of cross compiling to
a compatible arch such as building for i386 on an amd64.
We need to enable building the dirent and gnulib sources for clang-cl,
as we are still using the Microsoft-style headers and lib's and CRT.
We need to also do this for the following, for similar reasoning:
-Symbol export (via __declspec(dllexport))
-Dependency discovery without pkg-config files
-long long and ssize_t detection
We do, however, enable the autoptr tests for clang-cl builds. Note that
at this point real MSVC builds are still better supported than clang-cl
builds, and it will likely remain so for at least the near future,
alhtough real MSVC builds of the GTK stack are consumable and are usable
by clang-cl.