C library check: silence warnings about GNU-style line markers

Clang 15 complains about GNU-style line markers (`# <number>` instead of
`#line <number>`), which we don't need to do anything about.

Fixes: diffblue#7525

Author: tautschnig

src/ansi-c/library_check.sh

@@ -14,7 +14,8 @@ for f in "$@"; do
     perl -p -i -e 's/(__atomic_)/s$1/' __libcheck.c
     $CC -std=gnu99 -E -include library/cprover.h -D__CPROVER_bool=_Bool -D__CPROVER_thread_local=__thread -DLIBRARY_CHECK -o __libcheck.i __libcheck.c
     $CC -S -Wall -Werror -pedantic -Wextra -std=gnu99 __libcheck.i \
-      -o __libcheck.s -Wno-unused-label -Wno-unknown-pragmas
+      -o __libcheck.s -Wno-unused-label -Wno-unknown-pragmas \
+      -Wno-gnu-line-marker -Wno-unknown-warning-option
     ec="${?}"
     rm __libcheck.s __libcheck.i __libcheck.c
     [ "${ec}" -eq 0 ] || exit "${ec}"