Warning: Configuration logfiles contain indications of -Wimplicit-function-declaration

[Michael Newman]

Today I finally installed Big Sur and followed the MacPorts migration guide. I don't see any errors; no failures to build. However, I did get seven of these warnings:

Warning: Configuration logfiles contain indications of -Wimplicit-function-declaration; check that features were not accidentally disabled:

It was found in the following logs:

lynx2.8.9rel.1/config.log
clamav-0.103.2/config.log
anholt-libepoxy-d51a358/config.log
ghostpdl-9.54.0/config.log
graphviz-2.40.1/config.log
gst-libav-1.16.2/config.log
gst-plugins-bad-1.16.2/config.log

I have no idea what a "Wimplicit-function-declaration" is. I tried to search around, but was unable to enlighten myself. I gather it has something to do with C; about which I know nothing. If this warning is explained somewhere, please provide me with a link.

Do I need to do something about these, or are they ignorable?

Mike Newman
Korat, Thailand