Tests: compile with -lintl on Windows

Needed on MSYS2 for the MINGW32 target for some reason.

tests/SConscript

@@ -1,6 +1,7 @@
 Import('env', 'gegl_env')
 
 import os
+import sys
 
 testlib_env = env.Clone()
 
@@ -14,6 +15,8 @@ tests_sources = [fn for fn in os.listdir("./") if is_test(fn) and is_csource(fn)
 testlib_sources = [fn for fn in os.listdir("./") if not is_test(fn) and is_csource(fn)]
 
 testlib_env.Append(LIBS=['mypaint'])
+if sys.platform == 'win32':
+    testlib_env.Append(LIBS=['intl'])
 testlib_env.Append(CPPPATH=['../'], LIBPATH=['../'])
 
 if testlib_env['enable_gperftools']: