Remove AC_CONFIG_MACRO_DIR for non-existent `m4` directory

[wdconinc]

With the m4 directory removed (#76), the AC_CONFIG_MACRO_DIR results in an error.

     8     autoreconf: export WARNINGS=
     9     autoreconf: Entering directory '.'
     10    autoreconf: configure.ac: not using Gettext
     11    autoreconf: running: aclocal -I /home/software/spack/__spack_path_pl
           aceholder__/__spack_path_placeholder__/__spack_path_placeholder__/__
           spack_path_placeholder__/__spack_path_placeholder__/__spack_path_pla
           ceholder__/__spack_path_placeholder__/__spack_path_placeholder__/__s
           pack_path_placeh/linux-x86_64_v3/libtool-2.4.7-pkrzmj3exucbqdwkqidyc
           6czgjmbz4hs/share/aclocal -I /usr/share/aclocal --force -I m4
  >> 12    aclocal: error: couldn't open directory 'm4': No such file or direct
           ory
  >> 13    autoreconf: error: aclocal failed with exit status: 1

Ref: https://gitlab.spack.io/spack/spack-packages/-/jobs/19061060

[wdconinc]

FYI @mcarbonneaux