Fix asserts to not break refcounting

They were handled as a "assert 0; jump to loop that doesn't return".
Instead, just allow "assert 0" to be a block terminator.

src/codegen/irgen/irgenerator.cpp

@@ -1996,6 +1996,9 @@ private:
         }
         llvm::CallSite call = emitter.createCall(unw_info, g.funcs.assertFail, llvm_args);
         call.setDoesNotReturn();
+
+        emitter.getBuilder()->CreateUnreachable();
+        endBlock(DEAD);
     }
 
     void doAssign(AST_Assign* node, const UnwindInfo& unw_info) {

src/codegen/irgen/refcounts.cpp

@@ -361,6 +361,19 @@ static std::vector<llvm::BasicBlock*> computeTraversalOrder(llvm::Function* f) {
                 }
             }
 
+#ifndef NDEBUG
+            // This can currently get tripped if we generate an LLVM IR that has an infinite loop in it.
+            // This could definitely be supported, but I don't think we should be generating those cases anyway.
+            if (!best) {
+                for (auto& BB : ordering) {
+                    llvm::outs() << "added to " << BB->getName() << '\n';
+                }
+                for (auto& BB : *f) {
+                    if (added.count(&BB) == 0)
+                        llvm::outs() << "never got to " << BB.getName() << '\n';
+                }
+            }
+#endif
             assert(best);
             ordering.push_back(best);
             added.insert(best);

src/core/cfg.cpp

@@ -1673,13 +1673,6 @@ public:
         remapped->col_offset = node->col_offset;
         push_back(remapped);
 
-        CFGBlock* unreachable = cfg->addBlock();
-        unreachable->info = "unreachable";
-        pushJump(unreachable);
-
-        curblock = unreachable;
-        pushJump(unreachable, true);
-
         curblock = iftrue;
 
         return true;
@@ -2742,7 +2735,7 @@ CFG* computeCFG(SourceInfo* source, std::vector<AST_stmt*> body) {
         if (b->successors.size() == 0) {
             AST_stmt* terminator = b->body.back();
             assert(terminator->type == AST_TYPE::Return || terminator->type == AST_TYPE::Raise
-                   || terminator->type == AST_TYPE::Raise);
+                   || terminator->type == AST_TYPE::Raise || terminator->type == AST_TYPE::Assert);
         }
 
         if (b->predecessors.size() == 0) {