refs: work around gcc-11 warning with REF_HAVE_NEW

Using gcc-11 (or 12) to compile refs.o with -O3 results in: In file included from hashmap.h:4, from cache.h:6, from refs.c:5: In function ‘oidcpy’, inlined from ‘ref_transaction_add_update’ at refs.c:1065:3, inlined from ‘ref_transaction_update’ at refs.c:1094:2, inlined from ‘ref_transaction_verify’ at refs.c:1132:9: hash.h:262:9: warning: argument 2 null where non-null expected [-Wnonnull] 262 | memcpy(dst->hash, src->hash, GIT_MAX_RAWSZ); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from git-compat-util.h:177, from cache.h:4, from refs.c:5: refs.c: In function ‘ref_transaction_verify’: /usr/include/string.h:43:14: note: in a call to function ‘memcpy’ declared ‘nonnull’ 43 | extern void *memcpy (void *__restrict __dest, const void *__restrict __src, | ^~~~~~ That call to memcpy() is in a conditional block that requires REF_HAVE_NEW to be set. But in ref_transaction_update(), we make sure it isn't set coming in: if (flags & ~REF_TRANSACTION_UPDATE_ALLOWED_FLAGS) BUG("illegal flags 0x%x passed to ref_transaction_update()", flags); and then only set it if the variable isn't NULL: flags |= (new_oid ? REF_HAVE_NEW : 0) | (old_oid ? REF_HAVE_OLD : 0); So it should be impossible to reach that memcpy() with a NULL oid. But for whatever reason, gcc doesn't accept that hitting the BUG() means we won't go any further, even though it's marked with the noreturn attribute. And the conditional is correct; ALLOWED_FLAGS doesn't contain HAVE_NEW or HAVE_OLD, and you can even simplify it to check for those flags explicitly and the compiler still complains. We can work around this by just clearing the disallowed flags explicitly. This should be a noop because of the BUG() check, but it makes the compiler happy. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>