Enable -O2 in depends.py

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>

tests/scripts/depends.py

@@ -381,7 +381,7 @@ class DomainData:
 
     def __init__(self, options, conf):
         """Gather data about the library and establish a list of domains to test."""
-        build_command = [options.make_command, 'CFLAGS=-Werror']
+        build_command = [options.make_command, 'CFLAGS=-Werror -O2']
         build_and_test = [build_command, [options.make_command, 'test']]
         self.all_config_symbols = set(conf.settings.keys())
         # Find hash modules by name.