https://bugs.winehq.org/show_bug.cgi?id=56454
--- Comment #17 from sldev sldev@free.fr --- Silly me !!!
I found the cause of the build breakage...
Today, to diagnose a linking issue in another program, I switched the 'ld' alternative to ld.lld (the clang linker, which emits more verbose error messages); apparently, the latter does not work for compiling Wine (strange, still), and reverting to ld.bfd allows to build working Wine versions again...
Phew ! :-D