* 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)
The API is pretty specific to the implementationt details of the
self-hosted compiler. I don't want to have to independently support
and maintain this as part of the standard library, and be obligated
to not make breaking changes to it with changes to the implementation of
stage2.
