Disable the LICM pass for now.

There appear to be underlying problems with the way Cretonne handles value
aliases, which are causing problems for LICM. Disable LICM until we have
a chance to fix the underlying issues.

Fixes #275.

lib/cretonne/src/context.rs

@@ -92,8 +92,10 @@ impl Context {
         self.legalize(isa)?;
         if isa.flags().opt_level() == OptLevel::Best {
             self.compute_domtree();
+            /* TODO: Re-enable LICM.
             self.compute_loop_analysis();
             self.licm(isa)?;
+            */
             self.simple_gvn(isa)?;
         }
         self.compute_domtree();