Add -headerpad_max_install_names to darwin CROSSTOOL linker flags.

Fixes #1269

--
MOS_MIGRATED_REVID=122502116
diff --git a/tools/cpp/CROSSTOOL b/tools/cpp/CROSSTOOL
index 74a8d4e..5a23b58 100644
--- a/tools/cpp/CROSSTOOL
+++ b/tools/cpp/CROSSTOOL
@@ -217,6 +217,7 @@
   linker_flag: "-lstdc++"
   linker_flag: "-undefined"
   linker_flag: "dynamic_lookup"
+  linker_flag: "-headerpad_max_install_names"
   # TODO(ulfjack): This is wrong on so many levels. Figure out a way to auto-detect the proper
   # setting from the local compiler, and also how to make incremental builds correct.
   cxx_builtin_include_directory: "/"