upgrade to zig 0.13.0

[chrisirhc]

Disclaimer: No idea what I'm doing.

[chrisirhc]

Hit compilation errors which indicate that threads weren't turned on, when doing bazel test //test/c:test_libc_wasip1_wasm32 (when compiling on my Mac):

In file included from external/_main~toolchains~zig_sdk/lib/libcxx/src/barrier.cpp:9:
external/_main~toolchains~zig_sdk/lib/libcxx/include/barrier:51:4: error: "<barrier> is not supported since libc++ has been configured without support for threads."
   51 | #  error "<barrier> is not supported since libc++ has been configured without support for threads."
      |    ^
external/_main~toolchains~zig_sdk/lib/libcxx/src/condition_variable_destructor.cpp:26:3: error: unknown type name '__libcpp_condvar_t'
   26 |   __libcpp_condvar_t __cv_ = _LIBCPP_CONDVAR_INITIALIZER;
      |   ^
1 error generated.
Target //test/c:test_libc_wasip1_wasm32 failed to build
INFO: Elapsed time: 11.475s, Critical Path: 7.98s
INFO: 2 processes: 2 internal.

More similar errors around pthreads when using 0.14 nightlies (e.g. 0.14.0-dev.2271+f845fa04a) such as:

external/_main~toolchains~zig_sdk/lib/libcxx/include/__thread/support/pthread.h:18:10: error: 'pthread.h' file not found with <angled> include; use "quotes" instead
   18 | #include <pthread.h>
      |          ^
external/_main~toolchains~zig_sdk/lib/libcxx/include/__thread/support/pthread.h:47:9: error: unknown type name 'pthread_mutex_t'
   47 | typedef pthread_mutex_t __libcpp_mutex_t;
      |         ^