meson: Fix support for Windows and macOS
Hi @tpm,
This is the second part of the update. Here I've addressed the following:
- added all the missing checks for headers, functions, and semantics
- added the bundled libintl which provides some functions that are used under the hood on Windows and macOS (if gettext is not available)
- fixed some build and runtime issues known to happen under Windows (patches courtesy of the MSYS2 project, and adjusted here for consistency)
To help users in comparing and contrasting builds, I also regenerated the autotools files. By far it is the noisiest of the commits, let me know if you'd prefer it to be dropped.
This MR should be merged after !1 (merged) to make it use the correct runners. That commit is also duplicated here since I sent the MRs from a common branch.