Also install host-cpu-c-abi.m4 from gettext-tools/gnulib-m4

This fixes errors about gl_HOST_CPU_C_ABI_32BIT not being defined when
running autoreconf, and errors about such a command not being found when
the generated configure script is run.

configure.ac:20: warning: gl_HOST_CPU_C_ABI_32BIT is m4_require'd but not m4_defun'd

Based on only a cursory understanding of autoconf, it seems like all
the files in share/aclocal are always included. Therefore it should be
possible to detect errors like this by running autoconf or autoreconf,
before committing to pkgsrc.

(kim)