Enable the IL verifier by default.

Change the default value for the "enable_verifier" setting so the
verifier runs unless it is explicitly disabled.

Most projects using Cretonne are best off running the verifier always
until they start caring about compile time performance. Then they can
easily disable the verifier.

lib/cretonne/meta/base/settings.py

@@ -24,7 +24,8 @@ enable_verifier = BoolSetting(
 
         This makes compilation slower but catches many bugs. The verifier is
         disabled by default, except when reading Cretonne IL from a text file.
-        """)
+        """,
+        default=True)
 
 is_64bit = BoolSetting("Enable 64-bit code generation")