Begin mapping os.Error in the rest of the codebase

core/prof/spall/spall_windows.odin

@@ -12,7 +12,7 @@ MAX_RW :: 1<<30
 @(no_instrumentation)
 _write :: proc "contextless" (fd: os.Handle, data: []byte) -> (int, os.Error) #no_bounds_check /* bounds check would segfault instrumentation */ {
 	if len(data) == 0 {
-		return 0, os.ERROR_NONE
+		return 0, nil
 	}
 
 	single_write_length: win32.DWORD
@@ -25,12 +25,11 @@ _write :: proc "contextless" (fd: os.Handle, data: []byte) -> (int, os.Error) #n
 
 		e := win32.WriteFile(win32.HANDLE(fd), &data[total_write], to_write, &single_write_length, nil)
 		if single_write_length <= 0 || !e {
-			err := os.Platform_Error(win32.GetLastError())
-			return int(total_write), err
+			return int(total_write), os.get_last_error()
 		}
 		total_write += i64(single_write_length)
 	}
-	return int(total_write), os.ERROR_NONE
+	return int(total_write), nil
 }
 
 @(no_instrumentation)