Revert "Revert "FORTIFY_SOURCE: fortify strchr""

This reverts commit 0289342fe7adf762f218ddeb19fd02cb18da3f4a.
Revert "Revert "FORTIFY_SOURCE: fortify strrchr""

This reverts commit 3d59db8ee8c0a06e37d0fa564dbfbc8388f970ad.