* gcc.c (option_map): Add --coverage.
	(LINK_COMMAND_SPEC): Pass -lgcov for `coverage'.
	(cc1_options): Pass -fprofile-arcs -ftest-coverage for `coverage'.
	* config/darwin.h: Pass -lgcov for `coverage'.
	* doc/invoke.texi (Debugging Options): Document --coverage.

From-SVN: r95878