Workaround for the "terminator in middle of basic block" issue

The problem is that we emit an llvm "unreachable" instruction, and then
continue to emit other code, which fails the verifier.

endBlock(DEAD) is supposed to be the right way to handle that, but there
is some more work that would need to be done there to get that working
properly.

So just do the easy thing for now -- create a new BB so that it's ok to
emit more code.

src/codegen/irgen/irgenerator.cpp

@@ -923,9 +923,16 @@ private:
                     // trigger an exception, but the irgenerator will know that definitely-defined
                     // local symbols will not throw.
                     emitter.getBuilder()->CreateUnreachable();
+
+                    // Hacky: create a new BB for any more code that we might generate
+                    llvm::BasicBlock* continue_bb
+                        = llvm::BasicBlock::Create(g.context, "cant_reach", irstate->getLLVMFunction());
+                    emitter.setCurrentBasicBlock(continue_bb);
+
                     exc_type = exc_value = exc_tb = undefVariable();
-                    // TODO: should we not emit the rest of the block? I (kmod) think I tried that and
-                    // ran into some sort of issue, but I don't remember what it was.
+                    // TODO: we should just call endBlock instead.  It looks like the implementation
+                    // of that has some issues though, and it might end up generating code as well.  ANd
+                    // then I'm not sure that the higher-level irgen.cpp would handle that well.
                     // endBlock(DEAD);
                 }