[g]libtoolize looks for m4 using the environment variable M4. When that isn't set, it looks for m4 in PATH. However, when libtool is a build dependency but m4 is not, m4 will not be found in PATH. Since it is currently not set in the environment by superenv, this causes some builds to fail. Closes https://github.com/Homebrew/homebrew-core/pull/73932.
Library
This directory contains all the code run by the official brew command in Homebrew and all formulae (package descriptions) in taps (repositories containing formulae) in Taps subdirectories.