Do not include math-barriers.h in math_private.h.

This patch continues the math_private.h cleanup by stopping
math_private.h from including math-barriers.h and making the users of
the barrier macros include the latter header directly.  No attempt is
made to remove any math_private.h includes that are now unused, except
in strtod_l.c where that is done to avoid line number changes in
assertions, so that installed stripped shared libraries can be
compared before and after the patch.  (I think the floating-point
environment support in math_private.h should also move out - some
architectures already have fenv_private.h as an architecture-internal
header included from their math_private.h - and after moving that out
might be a better time to identify unused math_private.h includes.)

Tested for x86_64 and x86, and tested with build-many-glibcs.py that
installed stripped shared libraries are unchanged by the patch.

	* sysdeps/generic/math_private.h: Do not include
	<math-barriers.h>.
	* stdlib/strtod_l.c: Include <math-barriers.h> instead of
	<math_private.h>.
	* math/fromfp.h: Include <math-barriers.h>.
	* math/math-narrow.h: Likewise.
	* math/s_nextafter.c: Likewise.
	* math/s_nexttowardf.c: Likewise.
	* sysdeps/aarch64/fpu/s_llrint.c: Likewise.
	* sysdeps/aarch64/fpu/s_llrintf.c: Likewise.
	* sysdeps/aarch64/fpu/s_lrint.c: Likewise.
	* sysdeps/aarch64/fpu/s_lrintf.c: Likewise.
	* sysdeps/i386/fpu/s_nextafterl.c: Likewise.
	* sysdeps/i386/fpu/s_nexttoward.c: Likewise.
	* sysdeps/i386/fpu/s_nexttowardf.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_atan2.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_atanh.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_exp.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_exp2.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_j0.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_sqrt.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_expm1.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_fma.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_fmaf.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_log1p.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_nearbyint.c: Likewise.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c: Likewise.
	* sysdeps/ieee754/flt-32/e_atanhf.c: Likewise.
	* sysdeps/ieee754/flt-32/e_j0f.c: Likewise.
	* sysdeps/ieee754/flt-32/s_expm1f.c: Likewise.
	* sysdeps/ieee754/flt-32/s_log1pf.c: Likewise.
	* sysdeps/ieee754/flt-32/s_nearbyintf.c: Likewise.
	* sysdeps/ieee754/flt-32/s_nextafterf.c: Likewise.
	* sysdeps/ieee754/k_standardl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/e_asinl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/e_expl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/e_powl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_fmal.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_nearbyintl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_nextafterl.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_nexttoward.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_nexttowardf.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/e_asinl.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_fmal.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_rintl.c: Likewise.
	* sysdeps/ieee754/ldbl-96/e_atanhl.c: Likewise.
	* sysdeps/ieee754/ldbl-96/e_j0l.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_fma.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_fmal.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_nexttoward.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_nexttowardf.c: Likewise.
	* sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c: Likewise.
	* sysdeps/m68k/m680x0/fpu/s_nextafterl.c: Likewise.

sysdeps/generic/math_private.h

@@ -262,8 +262,6 @@ extern double __mpsin (double __x, double __dx, bool __range_reduce);
 extern double __mpcos (double __x, double __dx, bool __range_reduce);
 extern void __docos (double __x, double __dx, double __v[]);
 
-#include <math-barriers.h>
-
 /* The standards only specify one variant of the fenv.h interfaces.
    But at least for some architectures we can be more efficient if we
    know what operations are going to be performed.  Therefore we