that's not how it's working.  we see libintl.so get built & installed even when we pass --without-included-gettext.

you can find extended build logs here:
  https://bugs.gentoo.org/564168

the testsuite angle is already handled further down in the file:
http://git.savannah.gnu.org/cgit/gettext.git/tree/gettext-runtime/m4/gettext.m4?id=v0.19.8#n349

in Gentoo, i ended up just deleting lines 259 & 260 that checked the $PACKAGE name.

when building gettext on a system that has libintl (whether from gettext or elsewhere), passing the --without-included-gettext option is ignored.  this makes it a pain to build just the tools, or to maintain libintl as a sep package from gettext.

the problematic snippet is centered here:
http://git.savannah.gnu.org/cgit/gettext.git/tree/gettext-runtime/m4/gettext.m4?id=v0.19.8#n253
        dnl If an already present or preinstalled GNU gettext() is found,
        dnl use it.  But if this macro is used in GNU gettext, and GNU
        dnl gettext is already preinstalled in libintl, we update this
        dnl libintl.  (Cf. the install rule in intl/Makefile.in.)
        if { eval "gt_val=\$$gt_func_gnugettext_libc"; test "$gt_val" = "yes"; } \
           || { { eval "gt_val=\$$gt_func_gnugettext_libintl"; test "$gt_val" = "yes"; } \
                && test "$PACKAGE" != gettext-runtime \
                && test "$PACKAGE" != gettext-tools; }; then
          gt_use_preinstalled_gnugettext=yes
        else
          ...
        fi

    ifelse(gt_included_intl, yes, [
        if test "$gt_use_preinstalled_gnugettext" != "yes"; then
          dnl GNU gettext is not found in the C library.
          dnl Fall back on included GNU gettext library.
          nls_cv_use_gnu_gettext=yes
        fi
      fi

      if test "$nls_cv_use_gnu_gettext" = "yes"; then
        dnl Mark actions used to generate GNU NLS library.
        BUILD_INCLUDED_LIBINTL=yes
        USE_INCLUDED_LIBINTL=yes

since libintl is part of gettext-runtime, gt_use_preinstalled_gnugettext is set, which cascades into setting BUILD_INCLUDED_LIBINTL all the time, which cascades into installing it.

if we back up a bit to where the configure flag is checked:
http://git.savannah.gnu.org/cgit/gettext.git/tree/gettext-runtime/m4/gettext.m4?id=v0.19.8#n125
    gt_use_preinstalled_gnugettext=no
    ifelse(gt_included_intl, yes, [
      AC_MSG_CHECKING([whether included gettext is requested])
      AC_ARG_WITH([included-gettext],
        [  --with-included-gettext use the GNU gettext library included here],
        nls_cv_force_use_gnu_gettext=$withval,
        nls_cv_force_use_gnu_gettext=no)
      AC_MSG_RESULT([$nls_cv_force_use_gnu_gettext])

      nls_cv_use_gnu_gettext="$nls_cv_force_use_gnu_gettext"
      if test "$nls_cv_force_use_gnu_gettext" != "yes"; then
    ])

perhaps the right answer is to change the 4th arg to AC_ARG_WITH to:
  nls_cv_force_use_gnu_gettext=auto

and then change the if test below to:
      if test "$nls_cv_force_use_gnu_gettext" = "auto"; then