rtl.h (RTL_FLAG_CHECK*): Add an argument for the macro name, and use it in all invocations of these macros.

	* rtl.h (RTL_FLAG_CHECK*): Add an argument for the macro name,
	and use it in all invocations of these macros.  Clean up comments.
	* rtl.c (rtl_check_failed_flag): Add an argument for the name
	of the flag access macro whose check failed.
	* doc/rtl.texi (Flags): Document additional flag uses.

From-SVN: r53306