Mark cmake-data as Multi-Arch: foreign.

Closes: #973392

debian/changelog

@@ -1,8 +1,12 @@
 cmake (3.18.4-2) UNRELEASED; urgency=medium
 
+  [ Helmut Grohne ]
   * Drop unused Build-Depends: libbz2-dev and liblzma-dev. (Closes: #981135)
     Compression support is handled via libarchive.
 
+  [ Felix Geyer ]
+  * Mark cmake-data as Multi-Arch: foreign. (Closes: #973392)
+
  -- Helmut Grohne <helmut@subdivi.de>  Tue, 26 Jan 2021 16:54:47 +0100
 
 cmake (3.18.4-1) unstable; urgency=medium

debian/control

@@ -50,6 +50,7 @@ Description: cross-platform, open-source make system
 
 Package: cmake-data
 Architecture: all
+Multi-Arch: foreign
 Depends: ${misc:Depends}
 Description: CMake data files (modules, templates and documentation)
  This package provides CMake architecture independent data files (modules,