compat: enforce distinguishable file names in symbol table

compat: enforce distinguishable file names in symbol table

To make it possible to tell apart the static symbols in files built a
second time for compat guest support, arrange for their source file
names to be prefixed by a suitable path. We can't do this without
explicit .file directives, since gcc has always been stripping paths
from file names handed to the internally generated .file directive.
However, we can leverage __FILE__ if we make sure the second instance
gets compiled out of other than the very directory the wrapper sits in.

Where suitable, remove the long redundant explicit inclusions of
xen/config.h at once.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>