Implement `os.cpus` for Darwin (OS X) (#2115)

* adding experimental Mac implementation os os.cpus

* Simplify cpus interfaces

* remove support for osx 10

* Refactor os.cpus implementation

This commit substantially refactors how the Linux and Darwin implementations of
 `os.cpus`.  The goal is to avoid unnecessary copying and allow broader latitude
 in responding to errors per implementation.

* improved comments

* ensure no buffer overrun

* use PROCESSOR_CPU_LOAD_INFO_COUNT; not sure if this is correct

* oh teh noes

* use sliceTo instead of span

* cpu_ticks are uints

1 files changed, 17 insertions, 0 deletions

diff --git a/src/darwin_c.zig b/src/darwin_c.zig
index 474e3374f..f2e22c85e 100644
--- a/src/darwin_c.zig
+++ b/src/darwin_c.zig
@@ -550,6 +550,23 @@ pub fn get_system_loadavg() [3]f64 {
     };
 }
 
+pub const processor_flavor_t = c_int;
+
+// https://opensource.apple.com/source/xnu/xnu-792/osfmk/mach/processor_info.h.auto.html
+pub const PROCESSOR_CPU_LOAD_INFO: processor_flavor_t = 2;
+// https://opensource.apple.com/source/xnu/xnu-792/osfmk/mach/machine.h.auto.html
+pub const CPU_STATE_MAX = 4;
+pub const processor_cpu_load_info = extern struct {
+    cpu_ticks: [CPU_STATE_MAX]c_uint,
+};
+pub const PROCESSOR_CPU_LOAD_INFO_COUNT = @as(std.c.mach_msg_type_number_t,
+                                              @sizeOf(processor_cpu_load_info)/@sizeOf(std.c.natural_t));
+pub const processor_info_array_t = [*]c_int;
+pub const PROCESSOR_INFO_MAX = 1024;
+
+pub extern fn host_processor_info(host: std.c.host_t , flavor: processor_flavor_t , out_processor_count: *std.c.natural_t , out_processor_info: *processor_info_array_t, out_processor_infoCnt: *std.c.mach_msg_type_number_t) std.c.E;
+
+
 pub extern fn getuid(...) std.os.uid_t;
 pub extern fn getgid(...) std.os.gid_t;