port elisp-compilation support to emacs-23.1 and newer

port elisp-compilation support to emacs-23.1 and newer

In May of 2017, emacs.master support for using the long-deprecated
byte-compile-dest-file function was removed, and that removal broke
automake's elisp-compiling rule for any .el file not in the current
directory.  In emacs-23.1 (July 2009) byte-compile-dest-file-function
became the recommended way to adjust the byte-compiler's destination.
The removed functionality has been restored for Emacs-26, albeit with
dissuasive diagnostics warning about the imminent removal of this
functionality.  It will be removed in Emacs-27.
* lib/am/lisp.am (.el.elc): Use byte-compile-dest-file-function, rather
than byte-compile-dest-file.  Also, use "-f batch-byte-compile '$<'"
rather than open-coding it, as suggested by Glenn Morris.
* t/lisp-readonly-srcdir.sh: New file, to test for the above.
* t/list-of-tests.mk (handwritten_TESTS): Add it.
* NEWS (Bugs fixed): Mention this problem.