Fix Windows static build

On Windows, static compilation needs G_INTL_STATIC_COMPILATION
to be also defined during compilation. Else functions are exported with
__declspec(dllexport) which causes issues when importing symbols during
linkage with the static library.

meson.build

@@ -5,6 +5,10 @@ project('proxy-libintl', 'c',
  'c_std=gnu99',
  'buildtype=debugoptimized' ])
 
+if get_option('default_library') == 'static'
+ add_project_arguments('-DG_INTL_STATIC_COMPILATION', language : 'c')
+endif
+
 install_headers('libintl.h')
 
 intl_lib = library('intl',