gOlogy: skip dbranch at -Og

gOlogy: skip dbranch at -Og

Delayed slot filling moves insns without any regard to variable
location notes, causing the location information in them to become
incorrect.

Fixing that appears to be quite difficult, but filling delay slots is
hardly an essential optimization to run at -Og, so if the user wants
to privilege debuggability, skip delay slot filling.

for  gcc/ChangeLog

	* opts.c (default_options_table): Do not enable
	OPT_fdelayed_branch at -Og.
	* doc/invoke.texi (-fdelayed-branch): Document it.

From-SVN: r265708