testsuite: Adjust nextafter and skip profile-info-section on AIX.

testsuite: Adjust nextafter and skip profile-info-section on AIX.

nextafter-2.c builds nextafter-1.c with math.h, but nextafter-1.c
provides prototypes for the functions.  The prototypes can conflict
with the definitions in math.h.  This patch omits the prototypes
when compiling nextafer-2.c.

profile-info-section.c uses the profile-info-section flag that is not
valid on AIX, so skip the test on AIX.

gcc/testsuite/ChangeLog:

	* gcc.dg/nextafter-1.c: Omit prototypes if _NEXT_AFTER_2 defined.
	* gcc.dg/nextafter-2.c: Define _NEXT_AFTER_2.
	* gcc.dg/profile-info-section.c: Skip on AIX.