c-typeck.c (parser_build_binary_op): Condition warnings for X<=Y<=Z on -Wparentheses instead of -Wextra.

	* c-typeck.c (parser_build_binary_op): Condition warnings for
	X<=Y<=Z on -Wparentheses instead of -Wextra.
	* doc/invoke.texi: Update.  Document that most of -Wparentheses is
	supported for C only.

testsuite:
	* gcc.dg/Wparentheses-2.c, gcc.dg/Wparentheses-3.c,
	gcc.dg/Wparentheses-4.c, Wparentheses-5.c, Wparentheses-6.c,
	Wparentheses-7.c, Wparentheses-8.c, Wparentheses-9.c: New tests.

From-SVN: r84860