Create and use first-versions.h with macros for function symbol versions.

Create and use first-versions.h with macros for function symbol versions.

This patch arranges for the glibc build to generate a header
first-versions.h that defines macros for the earliest symbol version
in which each public symbol (GLIBC_[0-9]* symbol version, name only
uses C identifier characters) is available.

This is used in sysdeps/ieee754/ldbl-opt/math-type-macros-double.h to
replace the manually defined LDOUBLE_*_libm_version macros for various
functions defined using type-generic templates, the purpose of which
is to use in LONG_DOUBLE_COMPAT tests "was this function originally
added before glibc supported long double != double on this platform?".
As discussed in
<https://sourceware.org/ml/libc-alpha/2016-12/msg00246.html>, I expect
this to be useful more generally in reducing the amount of
special-case code needed in ldbl-opt and ldbl-64-128.

Tested with build-many-glibcs.py that installed stripped shared
libraries are unchanged by this patch.

	* scripts/versions.awk: Generate first-versions.h.
	* sysdeps/ieee754/ldbl-opt/math-type-macros-double.h: Include
	<first-versions.h>.
	(LDOUBLE_cabsl_libm_version): Remove macro.
	(LDOUBLE_cargl_libm_version): Likewise.
	(LDOUBLE_cimagl_libm_version): Likewise.
	(LDOUBLE_conjl_libm_version): Likewise.
	(LDOUBLE_creall_libm_version): Likewise.
	(LDOUBLE_cacosl_libm_version): Likewise.
	(LDOUBLE_cacoshl_libm_version): Likewise.
	(LDOUBLE_ccosl_libm_version): Likewise.
	(LDOUBLE_ccoshl_libm_version): Likewise.
	(LDOUBLE_casinl_libm_version): Likewise.
	(LDOUBLE_csinl_libm_version): Likewise.
	(LDOUBLE_casinhl_libm_version): Likewise.
	(LDOUBLE_csinhl_libm_version): Likewise.
	(LDOUBLE_catanl_libm_version): Likewise.
	(LDOUBLE_catanhl_libm_version): Likewise.
	(LDOUBLE_ctanl_libm_version): Likewise.
	(LDOUBLE_ctanhl_libm_version): Likewise.
	(LDOUBLE_cexpl_libm_version): Likewise.
	(LDOUBLE_clogl_libm_version): Likewise.
	(LDOUBLE_cprojl_libm_version): Likewise.
	(LDOUBLE_csqrtl_libm_version): Likewise.
	(LDOUBLE_cpowl_libm_version): Likewise.
	(LDOUBLE_clog10l_libm_version): Likewise.
	(LDOUBLE___clog10l_libm_version): Likewise.
	(LDOUBLE_fdiml_libm_version): Likewise.
	(LDOUBLE_fmaxl_libm_version): Likewise.
	(LDOUBLE_fminl_libm_version): Likewise.
	(LDOUBLE_ilogbl_libm_version): Likewise.
	(LDOUBLE_nanl_libm_version): Likewise.
	[!M_LIBM_NEED_COMPAT] (M_LIBM_NEED_COMPAT): Use
	FIRST_VERSION_libm_* macros.
	[!declare_mgen_libm_compat] (declare_mgen_libm_compat): Likewise.
	* Makerules [$(build-shared) = yes && !avoid-generated]
	(before-compile): Add $(common-objpfx)first-versions.h.
	[$(build-shared) = yes && !avoid-generated]
	($(common-objpfx)first-versions.h): New target.
	($(common-objpfx)sysd-versions): Depend on and change to rule for
	building $(common-objpfx)versions.stmp.