Revert "Do basic block merging as the last step"

This reverts commit d84778a, which
caused some breakage. Also, it might well have been better placed (or
at least just as well placed) beforehand anyway.

src/spesh/optimize.c

@@ -3100,17 +3100,14 @@ void MVM_spesh_optimize(MVMThreadContext *tc, MVMSpeshGraph *g, MVMSpeshPlanned
     MVM_spesh_usages_remove_unused_deopt(tc, g);
     MVM_spesh_eliminate_dead_ins(tc, g);
 
+    merge_bbs(tc, g);
+
     /* Make a post-inline pass through the graph doing things that are better
      * done after inlinings have taken place. Note that these things must not
      * add new fact dependencies. Do a final dead instruction elimination pass
      * to clean up after it. */
     post_inline_pass(tc, g, g->entry);
     MVM_spesh_eliminate_dead_ins(tc, g);
-
-    /* Merge basic blocks where possible, to aid the expression JIT, which is
-     * limited to one basic block. */
-    merge_bbs(tc, g);
-
 #if MVM_SPESH_CHECK_DU
     MVM_spesh_usages_check(tc, g);
 #endif