Add uvm32_useBreak(uvmst, bool) function to enable ebreak handling.

This is used in host-gdbstub to enable the functionality.

This allows the stackoverflow test to continue working. Meter test modified to handle new evt type.

hosts/host-gdbstub/host-gdbstub.c

@@ -58,6 +58,7 @@ int main(int argc, char *argv[]) {
   }
 
   uvm32_init(&vmst);
+  uvm32_useBreak(&vmst, true); // enable ebreak
 
   if (!uvm32_load(&vmst, rom, romlen)) {
     fprintf(stderr, "load failed!\n");