Update wasi-libc to 30094b6ed05f19cee102115215863d185f2db4f0.

 - Fix utimensat to avoid passing uninitialized values into WASI calls.
 - Optimize memcpy etc. using bulk-memory
 - Update to musl 1.2.3.
 - Fix `gettimeofday` to correctly handle a null argument.
 - Remove support for `__original_main`. (#295)