meson: fix install failure on Windows if bindir is not in PATH

We try to run fc-cache as part of the install, which runs the fc-cache binary in the build directory. On Windows this might fail because nothing sets up the environment in such a way that Windows can find the libs required by fc-cache (unless by luck we are operating in an environment where the install bindir is already in PATH, but this is not guaranteed).

Ideally Meson should set up the environment properly here, but currently it doesn't do that, so until it does we need to work around this problem somehow.

For now we simply ignore any fc-cache failures on Windows and print a big warning message. We have to suppress the dialog boxes that pop up when a DLL is not found in order to make this work nicely. This isn't pretty, but seems that least bad option for now.

See https://github.com/mesonbuild/meson/issues/8187

Fixes #260 (closed)