Module definition files may be useful when building with gcc on Windows also
(e.g. if the existing build uses them, if exports are aliased, if we were
retro enough to export by ordinal, etc.)
Add the .def file to the link command line when using gcc on Windows
Run the appropriate windows tests irrespective of compiler.
This detects and allows passing a generated file as a vs_module_def, it
also adds a testcase that tests using configure_file to generate the
.def file.
On MSVC, shared libraries only export symbols that have been explicitly exported
either as part of the symbol prototype or via a module definitions file.
On compilers other than MSVC, all symbols are exported in the shared library by
default and the format for the list of symbols to export is different, so this
is only used with the VisualStudio compiler.
The module defs file path can either be relative to the current source directory
or an absolute path using meson.source_root() + '/some/path'