Use ConfigParser instead of deprecated SafeConfigParser

Fixes this annoying warning while running the tests:

mesonbuild/coredata.py:237: DeprecationWarning: The SafeConfigParser
class has been renamed to ConfigParser in Python 3.2. This alias will be
removed in future versions. Use ConfigParser directly instead.

mesonbuild/coredata.py

@@ -234,7 +234,7 @@ def load_configs(filenames):
 
             raise MesonException('Cannot find specified native file: ' + f)
 
-    config = configparser.SafeConfigParser()
+    config = configparser.ConfigParser()
     config.read(gen())
     return config