formula_cellar_checks: check keg for mismatched arches

There have been a few instances I've noticed that we've been silently
installing binaries built for x86_64 on ARM. There's probably more that
I haven't found yet, so it seems useful to check this with an audit.

Library/Homebrew/formula_cellar_checks.rb

@@ -314,6 +314,22 @@ module FormulaCellarChecks
     "No `cpuid` instruction detected. #{formula} should not use `ENV.runtime_cpu_detection`."
   end
 
+  def check_binary_arches(formula)
+    return unless formula.prefix.directory?
+
+    keg = Keg.new(formula.prefix)
+    mismatches = keg.binary_executable_or_library_files.reject do |file|
+      file.arch == Hardware::CPU.arch
+    end
+    return if mismatches.empty?
+
+    <<~EOS
+      Binaries built for a non-native architecture were installed into #{formula}'s prefix.
+      The offending files are:
+        #{mismatches * "\n        "}
+    EOS
+  end
+
   def audit_installed
     @new_formula ||= false
 
@@ -334,6 +350,7 @@ module FormulaCellarChecks
     problem_if_output(check_plist(formula.prefix, formula.plist))
     problem_if_output(check_python_symlinks(formula.name, formula.keg_only?))
     problem_if_output(check_cpuid_instruction(formula))
+    problem_if_output(check_binary_arches(formula))
   end
   alias generic_audit_installed audit_installed
 

Library/Homebrew/os/mac/mach.rb

@@ -29,7 +29,7 @@ module MachOShim
 
       machos.each do |m|
         arch = case m.cputype
-        when :x86_64, :i386, :ppc64 then m.cputype
+        when :x86_64, :i386, :ppc64, :arm64, :arm then m.cputype
         when :ppc then :ppc7400
         else :dunno
         end