Restrict altered behavior to win. Dont annoy.

weasyprint/fonts.py

@@ -46,6 +46,10 @@ else:
         pangoft2 = dlopen(ffi, 'pangoft2-1.0', 'libpangoft2-1.0-0',
                           'libpangoft2-1.0.so', 'libpangoft2-1.0.dylib')
     except Exception as err:
+        # dont alter behavior on other platforms!
+        if not sys.platform.startswith('win'):
+            raise err
+        else:
             warnings.warn("'@font-face not supported: {0}".format(err))
             fontconfig = None
             pangoft2 = None