Move math_narrow_eval to separate math-narrow-eval.h.

Move math_narrow_eval to separate math-narrow-eval.h.

This patch continues cleaning up the math_private.h header, which
contains lots of different definitions many of which are only needed
by a limited subset of files using that header (and some of which are
overridden by architectures that only want to override selected parts
of the header), by moving the math_narrow_eval macro out to a separate
math-narrow-eval.h header, only included by those files that need it.
That header is placed in include/ (since it's used in stdlib/, not
just files built in math/, but no sysdeps variants are needed at
present).

Tested for x86_64, and with build-many-glibcs.py.  (Installed stripped
shared libraries change because of line numbers in assertions in
strtod_l.c.)

	* include/math-narrow-eval.h: New file.  Contents moved from ....
	* sysdeps/generic/math_private.h: ... here.
	(math_narrow_eval): Remove macro.  Moved to math-narrow-eval.h.
	[FLT_EVAL_METHOD != 0] (excess_precision): Likewise.
	* math/s_fdim_template.c: Include <math-narrow-eval.h>.
	* stdlib/strtod_l.c: Likewise.
	* sysdeps/i386/fpu/s_f32xaddf64.c: Likewise.
	* sysdeps/i386/fpu/s_f32xsubf64.c: Likewise.
	* sysdeps/i386/fpu/s_fdim.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_cosh.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_gamma_r.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_j1.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_jn.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_lgamma_r.c: Likewise.
	* sysdeps/ieee754/dbl-64/e_sinh.c: Likewise.
	* sysdeps/ieee754/dbl-64/gamma_productf.c: Likewise.
	* sysdeps/ieee754/dbl-64/k_rem_pio2.c: Likewise.
	* sysdeps/ieee754/dbl-64/lgamma_neg.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_erf.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_llrint.c: Likewise.
	* sysdeps/ieee754/dbl-64/s_lrint.c: Likewise.
	* sysdeps/ieee754/flt-32/e_coshf.c: Likewise.
	* sysdeps/ieee754/flt-32/e_exp2f.c: Likewise.
	* sysdeps/ieee754/flt-32/e_expf.c: Likewise.
	* sysdeps/ieee754/flt-32/e_gammaf_r.c: Likewise.
	* sysdeps/ieee754/flt-32/e_j1f.c: Likewise.
	* sysdeps/ieee754/flt-32/e_jnf.c: Likewise.
	* sysdeps/ieee754/flt-32/e_lgammaf_r.c: Likewise.
	* sysdeps/ieee754/flt-32/e_sinhf.c: Likewise.
	* sysdeps/ieee754/flt-32/k_rem_pio2f.c: Likewise.
	* sysdeps/ieee754/flt-32/lgamma_negf.c: Likewise.
	* sysdeps/ieee754/flt-32/s_erff.c: Likewise.
	* sysdeps/ieee754/flt-32/s_llrintf.c: Likewise.
	* sysdeps/ieee754/flt-32/s_lrintf.c: Likewise.
	* sysdeps/ieee754/ldbl-96/gamma_product.c: Likewise.