Related #4993 @theuni As far as I can tell it's only needed in this spot. Test bitcoin_bitcoin-qt seems to run fine.
I'm guessing because
OBJCXXLD qt/bitcoin-qt
CXXLD qt/test/test_bitcoin-qt
Related #4993
ACK. The issue here is that when automake encounters .mm files, it tags the final object as requiring an objective c++ linker. That shouldn't be a problem except that it doesn't communicate well with libtool.
I still haven't dug into where the communication breakdown is. I suspect that either it tells libtool to use the OBJCXX tag which libtool doesn't understand, or that automake itself doesn't have an OBJCXX tag case, so it just skips setting one.
Either way, manually specifying the CXX tag should be perfectly safe.
utACK