HEXL doesn't build on Mac
[ 37%] Built target coreobj
make[2]: *** No rule to make target `/usr/local/lib/libhexl.so', needed by `lib/libPALISADEcore.1.11.4.dylib'. Stop.
make[1]: *** [src/core/CMakeFiles/PALISADEcore.dir/all] Error 2
make: *** [all] Error 2'