Bootstrap asks user to install M4 when autoconf and m4 are missing

[rrthomas]

When autoconf is required but not installed, and M4 is also not installed, an error is generated saying that m4 should be installed.

This is technically correct, but it's confusing and unhelpful:

Confusing, because M4 may well not be listed as a build dependency of the project being built (for example, I list autoconf as a build dependency of my projects, knowing that autoconf requires M4).

Unhelpful, because for most users (who have the benefit of a package manager), the simplest solution is to install autoconf, which will in turn install M4. So it's not actually necessary manually to install M4 in most cases.