Disable FORTIFY_SOURCE when compiling without optims
Otherwise the build is cluttered with
```
/nix/store/fwpn2f7a4iqszyydw7ag61zlnp6xk5d3-glibc-2.30-dev/include/features.h:382:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp]
382 | # warning _FORTIFY_SOURCE requires compiling with optimization (-O)
| ^~~~~~~
```
when building with `OPTIMIZE=0`
This commit is contained in: