Snippets for cbmc 6.11.0 from FreeBSD 150amd64

Sourced from https://pkg-status.freebsd.org/beefy23/data/latest-per-pkg/cbmc/6.11.0/150amd64-default.log.

• __libcheck.c:314:32: warning: unknown warning group '-Wnonnull-compare', ignored [-Wunknown-warning-option]
    314 | #pragma GCC diagnostic ignored "-Wnonnull-compare"
        |                                ^