makefile: Defaults now show summary build commands and separate module compiles

- Invoking make with QUIET=0 (or in an exported environment variable)
  will display the full compile and link commands executed.
- Invoking make with BUILD_SEPARATE=0 will cause each simulator
  being built to be built with a single compile and link command.
  This is how things were previously, but now the default has been
  changed to more easily support active simulator development
  by compiling files that have changed.
- Silence link time warning on macOS
- cleanup C++ support for ND100 and C++ builds of other simulators

sim_disk.c

@@ -788,9 +788,7 @@ return filesystem_size;
 t_stat sim_disk_set_async (UNIT *uptr, int latency)
 {
 #if !defined(SIM_ASYNCH_IO)
-char *msg = "Disk: cannot operate asynchronously\r\n";
-sim_printf ("%s", msg);
-return SCPE_NOFNC;
+return sim_messagef (SCPE_NOFNC, "Disk: cannot operate asynchronously\n");
 #else
 struct disk_context *ctx = (struct disk_context *)uptr->disk_ctx;
 pthread_attr_t attr;