I'm having the exact same problem with both the PulseAudio and the ALSA plugin on Ubuntu with the build.linux64x64 squeak.cog.spur build.
Both self compiled and the binary releases of the plugins are not linked against the appropriate libraries, even when built with all the relevant headers and libraries available.
Looking at the plugin makefiles, it seems that the problem is that the plugin Makefile defines the link libraries in the (empty!) $LIBS define while autoconf puts them in the (unused) $PLIBS define.
If I hand edit the generated makefile so that it links using the right libraries, the plugin works correctly.
See attached for the generated Makefile with the PLIBS/LIBS error. [Makefile.txt](https://github.com/OpenSmalltalk/opensmalltalk-vm/files/3667916/Makefile.txt)
I tried tracing through this to see where this error occurs, but the autoconf stuff was too complex for me.