gdb, gdbserver, gdbsupport: fix some namespace comment formatting

I noticed a

  // namespace selftests

comment, which doesn't follow our comment formatting convention.  I did
a find & replace to fix all the offenders.

Change-Id: Idf8fe9833caf1c3d99e15330db000e4bab4ec66c

gdb/aarch64-linux-tdep.c

@@ -2972,7 +2972,7 @@ aarch64_linux_ltag_tests (void)
     }
 }
 
-} // namespace selftests
+} /* namespace selftests */
 #endif /* GDB_SELF_TEST */
 
 void _initialize_aarch64_linux_tdep ();