(More information was appended to PR pkg/53688 opened by Andreas
but I will try to summarize all possible details here too for
completeness, TLDR; emacs25-25.3nb10 and emacs26-26.1nb3 should
now works properly.)
Despite the buildlink3.mk change was needed it didn't solve the
problem originally reported by Riccardo.
Maya suggested to pass `-Wl,--verbose' to get more details about
the linking failures (by adding them to src/Makefile in `temacs$(EXEEXT):'
target) and indeed this pointed out the following: