glibc 2.28 breaks the current m4 release

[Paul Eggert]

glibc 2.28 was released today. Unfortunately it breaks the build of m4-1.4.18, 
the current release of GNU m4. This bug was reported some time ago, here:

https://lists.gnu.org/r/bug-gnulib/2018-03/msg00000.html

and fixed in Gnulib here:

https://github.com/coreutils/gnulib/commit/4af4a4a71827c0bc5e0ec67af23edef4f15cee8e#diff-5bcce8ce55246264586c4aed2a45ff89

so we need a new release of m4 pretty quickly. I can volunteer to do all the 
necessary changes to cut a new release, except that I suspect that I don't have 
the bits to actually publish it. Eric?