fuzz: OSS-fuzz build scripts into this repo

And also enable debug assertions to try and catch
more bugs.

Author: nathaniel-brough

fuzz/oss-fuzz-build.sh

@@ -0,0 +1,4 @@
+#!/bin/bash -eu
+cd $SRC/regex
+cargo fuzz build -O --debug-assertions 
+cp fuzz/target/x86_64-unknown-linux-gnu/release/fuzz_regex_match $OUT/