Memory unsafety: data races in darwin.c

[tmfink]

I've found the following data races in darwin.c:

1. The static unsigned long long size is a mutable global that is read/modified without any synchronization.

   • sys-info-rs/c/darwin.c

     Line 109 in 1c119b3

     static unsigned long long size = 0;

   • It looks like this is meant to be an optimization but it is unsound since it is called directly from the public Rust function mem_info(). Multiple Rust threads could racily write to the global variable size.
2. static int skipvfs is mutable global that is racily initizialized in makevfslist().

   • sys-info-rs/c/darwin.c

     Line 20 in 1c119b3

     static int skipvfs;

   • disk_info() is a public Rust function that can be directly called from safe Rust code