Linux: Ignore Debian-specific case when cross-compiling

When constructing settings for the target environment during cross
compiling we should not check for /etc/debian_version on the host.

Modules/Platform/Linux.cmake

@@ -52,6 +52,6 @@ include(Platform/UnixPaths)
 
 # Debian has lib64 paths only for compatibility so they should not be
 # searched.
-if(EXISTS "/etc/debian_version")
+if(NOT CMAKE_CROSSCOMPILING AND EXISTS "/etc/debian_version")
   set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS FALSE)
 endif()