[Ada] Avoid spurious warning on wrong order of operator call arguments

[Ada] Avoid spurious warning on wrong order of operator call arguments

GNAT issues a warning under -gnatwa when actuals for a call are named
like the formals, but in a different order. This is inappropriate for
calls to operators in infix form, when e.g. Right <= Left is in general
the intended order. Special case calls to operators to avoid that
spurious warning.

2019-07-11  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* sem_res.adb (Check_Argument_Order): Special case calls to
	operators.

gcc/testsuite/

	* gnat.dg/warn21.adb, gnat.dg/warn21.ads: New testcase.

From-SVN: r273378