This renames /opt/wasi/share/sysroot to /opt/wasi/share/wasi-sysroot.
If the user selects an alternate prefix, this allows wasi-sysroot to
coexist with other packages with less risk of namespace collision. For
example, if the user uses a prefix of /usr/local, this avoids using
/usr/local/share/sysroot, which is fairly generic, and uses
/usr/local/share/wasi-sysroot, which more clearly indicates its purpose.
The wasi-libc update here brings numerous bug fixes and minor changes,
and __wasilibc_rmfileat has been renamed to __wasilibc_unlinkat.
The only WebAssembly-relevant patch in the LLVM 8.0.1 update here is
4b1712f7, a fix for using /dev/null as the output file.
Libc++abi's verbose terminate handler is only useful when exceptions are
enabled. Disabling it removes a few hundred thousand bytes from many C++
programs.