meson: Use proxy-libintl if gettext is not found

This is a stub-only library that can be used while building against
MSVC and contains no i18n machinery at all.

The dependencies added indirectly use the libintl.h header, and when
built as a subproject, the header won't be in a path known the
pre-processor.

gio/meson.build

@@ -755,7 +755,7 @@ executable('gio', gio_tool_sources,
   c_args : ['-DHAVE_CONFIG_H=1'] + gio_c_args,
   # intl.lib is not compatible with SAFESEH
   link_args : noseh_link_args,
-  dependencies : [libgio_dep, libgobject_dep, libgmodule_dep, libglib_dep])
+  dependencies : [libintl, libgio_dep, libgobject_dep, libgmodule_dep, libglib_dep])
 
 executable('gresource', 'gresource-tool.c',
   install : true,

gio/win32/meson.build

@@ -10,5 +10,6 @@ giowin32_sources = [
 giowin32_lib = static_library('giowin32',
   sources : [giowin32_sources, gioenumtypes_h],
   include_directories : [configinc, glibinc, gioinc, gmoduleinc],
+  dependencies : [libintl],
   pic : true,
   c_args : [ '-DHAVE_CONFIG_H', '-DG_DISABLE_DEPRECATED' ] + gio_c_args)