That option is not mentioned in the man page of libtoolize 2.4.4.19-fda4.
Moveover, a comment in line 2623 says "--automake is for 1.5 compatibility".
This option is redundant now.
#
echo "buildconf: running libtoolize"
-${libtoolize} --copy --automake --force || die "libtoolize command failed"
+${libtoolize} --copy --force || die "libtoolize command failed"
# When using libtool 1.5.X (X < 26) we copy libtool.m4 to our local m4
# subdirectory and this local copy is patched to fix some warnings that