* 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)
