Add _FloatN, _FloatNx tests for __builtin_fpclassify.

Add _FloatN, _FloatNx tests for __builtin_fpclassify.

This patch adds tests for _FloatN and _FloatNx arguments to the
__builtin_fpclassify type-generic built-in function, omitted from the
original tests for type-generic functions on these types.

Tested for x86_64-pc-linux-gnu; all the supported new tests pass.

	* gcc.dg/torture/float128-tg-3.c, gcc.dg/torture/float128x-tg-3.c,
	gcc.dg/torture/float16-tg-3.c, gcc.dg/torture/float32-tg-3.c,
	gcc.dg/torture/float32x-tg-3.c, gcc.dg/torture/float64-tg-3.c,
	gcc.dg/torture/float64x-tg-3.c, gcc.dg/torture/floatn-tg-3.h: New
	tests.

From-SVN: r240328