Workaround this compile error for gcc by adding -Wno-narrowing for it:
spindle_logd.cc:65:76: error: narrowing conversion of '255' from 'int' to 'char'
spindle_logd.cc:65:76: error: narrowing conversion of '223' from 'int' to 'char'
spindle_logd.cc:65:76: error: narrowing conversion of '191' from 'int' to 'char'
spindle 0.8.1 wants to compile tests with mpi.h, newer versions need mpicc,
thus add: depends_on("mpi"). Spindle supports the --no-mpi to disable MPI.