ldbl-128ibm: Copy implementations from ldbl-128 instead of including them

Some files under sysdeps/ieee754/ldbl-128ibm/ are able to reuse the
implementation in sysdeps/ieee754/ldbl-128/ by defining _Float128 to
long double.  This relied on compiler support for _Float128 being
disabled.  On powerpc, such support was disabled by default, however, it
got enabled by default [1] in GCC 8.

This patch copies the implementations from ldbl-128 to ldbl-128ibm.  The
uses of _Float128 and L() are kept intact in this patch and are replaced
with a script in a subsequent patch.

[1] https://gcc.gnu.org/ml/gcc-patches/2017-08/msg01028.html

Tested for powerpc64 and powerpc64le.

	* sysdeps/ieee754/ldbl-128ibm/e_expl.c: Include tables from
	sysdeps/ieee754/ldbl-128ibm.
	* sysdeps/ieee754/ldbl-128ibm/e_j0l.c: Copy contents from the
	equivalent implementation in sysdeps/ieee754/ldbl-128/ instead
	of including it.  Keep _Float128 and L() intact.  These will be
	reviewed by a separate patch.
	* sysdeps/ieee754/ldbl-128ibm/e_j1l.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/e_lgammal_r.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/t_expl.h: Likewise.

(cherry picked from commit c5c2e667)