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 linker 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