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

core/os/os2/pipe_posix.odin

@@ -0,0 +1,37 @@
+//+private
+//+build darwin, netbsd, freebsd, openbsd
+package os2
+
+import "core:sys/posix"
+import "core:strings"
+
+_pipe :: proc() -> (r, w: ^File, err: Error) {
+	fds: [2]posix.FD
+	if posix.pipe(&fds) != .OK {
+		err = _get_platform_error()
+		return
+	}
+
+	r = __new_file(fds[0])
+	ri := (^File_Impl)(r.impl)
+
+	rname := strings.builder_make(file_allocator())
+	// TODO(laytan): is this on all the posix targets?
+	strings.write_string(&rname, "/dev/fd/")
+	strings.write_int(&rname, int(fds[0]))
+	ri.name  = strings.to_string(rname)
+	ri.cname = strings.to_cstring(&rname)
+
+	w = __new_file(fds[1])
+	wi := (^File_Impl)(w.impl)
+	
+	wname := strings.builder_make(file_allocator())
+	// TODO(laytan): is this on all the posix targets?
+	strings.write_string(&wname, "/dev/fd/")
+	strings.write_int(&wname, int(fds[1]))
+	wi.name  = strings.to_string(wname)
+	wi.cname = strings.to_cstring(&wname)
+
+	return
+}
+