os/mac: Allow MachO.dynamically_linked_libraries to be filtered by dylib type.

This allows us to filter out weak linkages during audits, preventing
a false error from occurring when the dylib cannot be found.

Library/Homebrew/os/mac/linkage_checker.rb

@@ -23,7 +23,10 @@ class LinkageChecker
     @keg.find do |file|
       next if file.symlink? || file.directory?
       next unless file.dylib? || file.mach_o_executable? || file.mach_o_bundle?
-      file.dynamically_linked_libraries.each do |dylib|
+
+      # weakly loaded dylibs may not actually exist on disk, so skip them
+      # when checking for broken linkage
+      file.dynamically_linked_libraries(except: :LC_LOAD_WEAK_DYLIB).each do |dylib|
         @reverse_links[dylib] << file
         if dylib.start_with? "@"
           @variable_dylibs << dylib

Library/Homebrew/os/mac/mach.rb

@@ -51,8 +51,10 @@ module MachO
     end
   end
 
-  def dynamically_linked_libraries
-    macho.linked_dylibs
+  def dynamically_linked_libraries(except: :none)
+    lcs = macho.dylib_load_commands.reject { |lc| lc.type == except }
+
+    lcs.map(&:name).map(&:to_s)
   end
 
   def dylib_id