[ARC] Update warning messges.

[ARC] Update warning messges.

When we pass an mcpu to the compiler we have two types of (hardware
configuration) flags that are set:

1. Architecture specific, for example code-density is always enabled
for ARCHS architectures. These options are overwriting whatever the
corresponding user options with the preset ones.

2. CPU specific, for example archs is using LL64 option by
default. These options can be freely enabled or disabled.

Because of the above complexity, we need to throw some errors for the
user to know when he/she does something which goes against the above
rules. Thus, I came up with the following set of rules:

1. Overwriting default architecture specific hardware option: it is
ignored, a warning is thrown;

2. Overwriting default CPU specific hardware option: it is taken into
account, a warning is thrown.

gcc/
2018-06-12  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc-arch.h: Update ARC_OPTX macro.
	* config/arc/arc-options.def (ARC_OPTX): Introduce a new doc
	field.
	* config/arc/arc.c (arc_init): Update pic warning.
	(irq_range): Update irq range parsing warnings.
	(arc_override_options): Update various warning messages.
	(arc_handle_aux_attribute): Likewise.

gcc/testsuite
2018-06-12  Claudiu Zissulescu  <claziss@synopsys.com>

	* gcc.target/arc/builtin_simdarc.c: Update test.
	* gcc.target/arc/mulsi3_highpart-2.c: Likewise.
	* gcc.target/arc/tumaddsidi4.c: Likewise.

From-SVN: r261495