Merge pull request #12069 from carlocab/bison-m4

superenv: set `M4` on Linux when `bison` is a dependency

Library/Homebrew/extend/os/linux/extend/ENV/super.rb

@@ -24,6 +24,7 @@ module Superenv
     self["HOMEBREW_OPTIMIZATION_LEVEL"] = "O2"
     self["HOMEBREW_DYNAMIC_LINKER"] = determine_dynamic_linker_path
     self["HOMEBREW_RPATH_PATHS"] = determine_rpath_paths(@formula)
+    self["M4"] = "#{HOMEBREW_PREFIX}/opt/m4/bin/m4" if deps.any? { |d| d.name == "libtool" || d.name == "bison" }
   end
 
   def homebrew_extra_paths