Update copying.awk for _initialize declaration patch

Update copying.awk for _initialize declaration patch

Commit 6c265988 ("gdb: add back declarations for _initialize
functions") modified copying.c, but not copying.awk.  This patch
updates copying.awk to backport the appropriate fix.  This way, if
copying.awk is run again, it will create the correct output.

I'm checking this in as obvious.