Allow disabling arch flag filtering

Closes Homebrew/homebrew#17352.

Library/ENV/4.3/cc

@@ -127,10 +127,15 @@ class Cmd
     loop do
       case arg = enum.next
       when "-arch"
-        enum.next
+        if cccfg?("K")
+          args << arg << enum.next
+        else
+          enum.next
+        end
       when "-m32"
-        args << arg if cccfg?("3")
+        args << arg if cccfg?("3") || cccfg?("K")
       when "-m64"
+        args << arg if cccfg?("K")
       when /^-Xarch_/
         refurbished = refurbish_arg(enum.next, enum)
         unless refurbished.empty?

Library/Homebrew/extend/ENV/shared.rb

@@ -239,4 +239,6 @@ module SharedEnvExtension
       EOS
     end
   end
+
+  def permit_arch_flags; end
 end

Library/Homebrew/extend/ENV/super.rb

@@ -81,6 +81,7 @@ module Superenv
     # x - Enable C++11 mode.
     # g - Enable "-stdlib=libc++" for clang.
     # h - Enable "-stdlib=libstdc++" for clang.
+    # K - Don't strip -arch <arch>, -m32, or -m64
     #
     # On 10.8 and newer, these flags will also be present:
     # s - apply fix for sed's Unicode support
@@ -266,6 +267,10 @@ module Superenv
     end
   end
 
+  def permit_arch_flags
+    append "HOMEBREW_CCCFG", "K"
+  end
+
   def cxx11
     case self["HOMEBREW_CC"]
     when "clang"