Fork fission bufferize

• Refactor fork fission, add fork fission bufferized version.
• Add test that uses fork fission to create extra forks.

hercules_cg/src/cpu.rs

@@ -694,7 +694,7 @@ impl<'a> CPUContext<'a> {
                         );
                         write!(
                             body,
-                            "  {} = call i64 @llvm.umin.i64(i64{},i64%dc{}))\n",
+                            "  {} = call i64 @llvm.umin.i64(i64{},i64%dc{})\n",
                             new_val,
                             cur_value,
                             x.idx()