Even though gettext is specified as a dependency for glib, for cross-compiling, we need libintl as a rdependency. In my case, with mingw32, dependencies (but not rdependencies) are ignored, libintl is not pulled in and configure fails at the libintl check (of course it is also a runtime dependency, since the dynamic libraries are needed at runtime).
Created attachment 441324 [details, diff] patch for glib ebuild
[master bcea1ef] dev-libs/glib: libpcre static-libs USE needs to be sync with glib (#588082 by Jordan Yelloz), libintl is needed (#589336 by Gerhard Bräunlich). 1 file changed, 1 insertion(+) rename dev-libs/glib/{glib-2.48.1.ebuild => glib-2.48.1-r1.ebuild} (99%)