Put build type warning flags at the beginning so they are overridable.

backends.py

@@ -202,10 +202,10 @@ class Backend():
     def generate_basic_compiler_args(self, target, compiler):
         commands = []
         commands += compiler.get_always_args()
-        commands += self.build.get_global_args(compiler)
-        commands += self.environment.coredata.external_args[compiler.get_language()]
         if self.environment.coredata.buildtype != 'plain':
             commands += compiler.get_std_warn_args()
+        commands += self.build.get_global_args(compiler)
+        commands += self.environment.coredata.external_args[compiler.get_language()]
         commands += target.get_extra_args(compiler.get_language())
         commands += compiler.get_buildtype_args(self.environment.coredata.buildtype)
         if self.environment.coredata.coverage: