Streamline dump control options

- Rename `--dump-treei` option to `--dumpi-tree`, which itself is now a
  special case of `--dumpi-<tag>` where tag can be a magic word, or a
  filename
- Control dumping via static `dump*()` functions, analogous to `debug()`
- Make dumping independent of the value of `debug()` (so dumping always
  works even without the debug flag)
- Add separate `--dumpi-graph` for dumping V3Graphs, which is again a
  special case of `--dumpi-<tag>`
- Alias `--dump-<tag>` to `--dumpi-<tag> 3` as before

src/V3Os.cpp

@@ -29,8 +29,13 @@
 #include "verilatedos.h"
 
 // Limited V3 headers here - this is a base class for Vlc etc
-#include "V3String.h"
 #include "V3Os.h"
+#include "V3String.h"
+
+#ifndef V3ERROR_NO_GLOBAL_
+#include "V3Global.h"
+VL_DEFINE_DEBUG_FUNCTIONS;
+#endif
 
 #include <cerrno>
 #include <climits>  // PATH_MAX (especially on FreeBSD)
@@ -38,6 +43,7 @@
 #include <dirent.h>
 #include <fstream>
 #include <memory>
+
 #include <sys/stat.h>
 #include <sys/types.h>