* caching system: use 16 bytes siphash final(), there was a bug in the
   std lib that wasn't catching undefined values for 18 bytes. fixed in
   master branch.
 * fix caching system unit test logic to not cause error.TextBusy on windows
 * port the logic from stage1 for building glibc shared objects
 * add is_native_os to the base cache hash
 * fix incorrectly freeing crt_files key (which is always a reference to
   global static constant data)
 * fix 2 use-after-free in loading glibc metadata
 * fix memory leak in buildCRTFile (errdefer instead of defer on arena)