os2: initial implementation for Darwin&BSDs, process API is only thing incomplete

core/os/os2/temp_file_posix.odin

@@ -0,0 +1,20 @@
+//+private
+//+build darwin, netbsd, freebsd, openbsd
+package os2
+
+import "base:runtime"
+
+@(require)
+import "core:sys/posix"
+
+_temp_dir :: proc(allocator: runtime.Allocator) -> (string, runtime.Allocator_Error) {
+	if tmp, ok := _lookup_env("TMPDIR", allocator); ok {
+		return tmp, nil
+	}
+
+	when #defined(posix.P_tmpdir) {
+		return clone_string(posix.P_tmpdir, allocator)
+	}
+
+	return clone_string("/tmp/", allocator)
+}