[gdb/build] Re-add *.[ch] in gdb.pot

In commit 4a40fe05bf0 ("[gdb/build] Handle gdbsupport and gdbserver in
gdb.pot"), in order to handle '*.cc' files I did:
...
-	  -name '*.[hc]' -print
+	  -name '*.[hc]' -o -name '*.cc' -print
...
but failed to understand that this no longer printed the '*.[hc]' names.

Fix this by adding a '-print' for '*.[hc]'.

Tested by doing:
...
$ cd build/gdb
$ make po/gdb.pot
 ...
$ grep -c symtab.c po/gdb.pot
102
...