Fix atanhl missing underflows (bug 16352).

Fix atanhl missing underflows (bug 16352).

Similar to various other bugs in this area, some atanh implementations
do not raise the underflow exception for subnormal arguments, when the
result is tiny and inexact.  This patch forces the exception in a
similar way to previous fixes.  (No change in this regard is needed
for the i386 implementation; special handling to force underflows in
these cases will only be needed there when the spurious underflows,
bug 18049, get fixed.)

Tested for x86_64, x86, powerpc and mips64.

	[BZ #16352]
	* sysdeps/i386/fpu/e_atanh.S (dbl_min): New object.
	(__ieee754_atanh): Force underflow exception for results with
	small absolute value.
	* sysdeps/i386/fpu/e_atanhf.S (flt_min): New object.
	(__ieee754_atanhf): Force underflow exception for results with
	small absolute value.
	* sysdeps/ieee754/dbl-64/e_atanh.c: Include <float.h>.
	(__ieee754_atanh): Force underflow exception for results with
	small absolute value.
	* sysdeps/ieee754/flt-32/e_atanhf.c: Include <float.h>.
	(__ieee754_atanhf): Force underflow exception for results with
	small absolute value.
	* sysdeps/ieee754/ldbl-128/e_atanhl.c: Include <float.h>.
	(__ieee754_atanhl): Force underflow exception for results with
	small absolute value.
	* sysdeps/ieee754/ldbl-128ibm/e_atanhl.c: Include <float.h>.
	(__ieee754_atanhl): Force underflow exception for results with
	small absolute value.
	* sysdeps/ieee754/ldbl-96/e_atanhl.c: Include <float.h>.
	(__ieee754_atanhl): Force underflow exception for results with
	small absolute value.
	* math/auto-libm-test-in: Do not allow missing underflow
	exceptions from atanh.
	* math/auto-libm-test-out: Regenerated.