/usr/lib/gcc/x86_64-linux-gnu/5/include/d/std/windows/iunknown.d is in libphobos-5-dev 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | // Written in the D programming language.
/// Please import core.sys.windows.com instead. This module will be deprecated in DMD 2.068.
module std.windows.iunknown;
// Replaced by:
public import core.sys.windows.com;
|