message: Be friendlier to unsupported compilers
diff: @@ -150,10 +150,13 @@ build-mpi: $(MPI_TARGETS)
  @echo '--- boost mpi bindings built ---'
  .PHONY: build
  -build: bin/stanc$(EXE) bin/stansummary$(EXE) bin/print$(EXE) bin/diagnose$(EXE) $(LIBSUNDIALS) $(MPI_TARGETS) $(STAN)src/stan/model/model_header.hpp.gch
  +build: bin/stanc$(EXE) bin/stansummary$(EXE) bin/print$(EXE) bin/diagnose$(EXE) $(LIBSUNDIALS) $(MPI_TARGETS)
  @echo ''
  @echo '--- CmdStan v$(CMDSTAN_VERSION) built ---'
  +ifeq ($(CXX_TYPE),clang)
  +build: $(STAN)src/stan/model/model_header.hpp.gch
  +endif
  ##
  # Clean up.
  