In Bullseye, gcc now passes the option '--as-needed' to the linker by default. This option allows the linker to ignore those libraries supplied on the command line whose symbols are not used by the lib or program being created; however, 'symbols used' are evaluated at that point in the command line, so this will work:

gcc -o dumb dumb.c -lprce

assuming dumb invokes a pcre lib function; this will not work:

gcc -lpcre -o dumb dumb.c

A quick fix was provided for 'ipaddrcheck' in commit 5d5be019 by passing '--no-as-needed'. A more proper fix is obtained by only adding linked libs to packagename_LDADD, instead of packagename_LDFLAGS, as mentioned here:

https://wiki.debian.org/ToolChain/DSOLinking#Unresolved_symbols_in_shared_libraries

The revised fix will be added to src/Makefile.am in ipaddrcheck