https://gcc.gnu.org/ml/gcc-patches/2018-04/msg01303.html
	* dumpfile.c (dump_open): Allow '-' for stdout.
	* doc/invoke.texi (Developer Options): Document dump filename
	determination early.  Document stdin/stdout selection.

Co-Authored-By: Sandra Loosemore <sandra@codesourcery.com>

From-SVN: r259760