Speedup bootstrap building gettext-tools with visual studio

gvsbuild has a port of gettext-tools for visual studio, this would reduce the bootstrap time in windows almost 3h, which is the time that gettext-tools takes to build:

https://github.com/wingtk/gvsbuild/blob/master/gvsbuild/projects.py#L451

This requires a new recipe for gettext-tools and win-inconv and a new MSBuild backend for Visual Studio projects.