arc/gcc: Better creation of __NPS400__ define

arc/gcc: Better creation of __NPS400__ define

The __NPS400__ define is currently created in CPP_SPEC unlike the other
target defines, which are created in arc-c.def.  Further, the current
__NPS400__ define is (currently) only created when -mcpu=nps400 is
passed, which is fine, except that if GCC is configured using
--with-cpu=nps400 then the -mcpu option is not required and the
__NPS400__ define will not be created.

This commit moves the __NPS400__ define into arc-c.def inline with all
of the other target defines, and removes the code in CPP_SPEC that used
to create the define.

In order to support the creation of the define in arc-c.def, a new
TARGET_NPS400 macro is created in arc.h.

gcc/ChangeLog:

	* config/arc/arc-c.def: Add __NPS400__ definition.
	* config/arc/arc.h (CPP_SPEC): Don't define __NPS400__ here.
	(TARGET_NPS400): Define.

From-SVN: r245294