m4 failure on OS X High Sierra, with patch

[George Hartzell]

Hi All,

I'm ensuring that the Spack packager can build m4 on OS X High Sierra.

Here's my PR for them:

    https://github.com/spack/spack/pull/8559

It's a repackaging of a patch from the Homebrew project's m4 recipe, here:

    https://github.com/Homebrew/homebrew-core/blob/master/Formula/m4.rb#L18-L25

I'm not sure if the issue was reported to you or not, so I am.

Thanks,

g.