Always pass -headerpad_max_install_names to the linker

We use install_name_tool pretty liberally, so we need to take steps to
ensure libraries and executables are always linked with this flag.

Closes Homebrew/homebrew#20233.
Fixes Homebrew/homebrew#17984.
Fixes Homebrew/homebrew#22078.

Library/ENV/4.3/cc

@@ -191,7 +191,12 @@ class Cmd
     syslibpath
   end
   def ldflags
-    libpath.to_flags('-L')
+    args = libpath.to_flags('-L')
+    case mode
+    when :ld   then args << '-headerpad_max_install_names'
+    when :ccld then args << '-Wl,-headerpad_max_install_names'
+    end
+    args
   end
   def cppflags
     sys, opt = cpath

Library/Homebrew/extend/ENV/std.rb

@@ -55,6 +55,8 @@ module Stdenv
     # Os is the default Apple uses for all its stuff so let's trust them
     set_cflags "-Os #{SAFE_CFLAGS_FLAGS}"
 
+    append 'LDFLAGS', '-Wl,-headerpad_max_install_names'
+
     # set us up for the user's compiler choice
     self.send self.compiler