Remove defaulted 'tid' parameter to ptid_t constructor

I wanted to find, and potentially modify, all the spots where the
'tid' parameter to the ptid_t constructor was used.  So, I temporarily
removed this parameter and then rebuilt.

In order to make it simpler to search through the "real" (nonzero)
uses of this parameter, something I knew I'd have to do multiple
times, I removed any ", 0" from constructor calls.

Co-Authored-By: John Baldwin <jhb@FreeBSD.org>

gdb/linux-fork.c

@@ -41,7 +41,7 @@
 struct fork_info
 {
   explicit fork_info (pid_t pid)
-    : ptid (pid, pid, 0)
+    : ptid (pid, pid)
   {
   }