Add style checks to check_GNU_style.sh.

Add style checks to check_GNU_style.sh.

gcc/contrib/ChangeLog:
2016-03-07  Martin Sebor  <msebor@redhat.com>

	* check_GNU_style.sh (color): New global variable.
	Add checks for trailing operators and spaces before left brackets.
	Tightened up a check for a trailing left curly brace.
	(g, ag, vg): Use color.
	(col): Don't complain about excessively long lines with DejaGnu
	directives.

From-SVN: r234035