build: allow to test clang .include without asm symlink

build: allow to test clang .include without asm symlink

The clang test for "asm()-s support .include." needs to be modified
because the symbolic link asm -> asm-x86 may not exist when the test
is runned. Since it's an x86 test, we don't need the link.

This will be an issue with the following patch "xen/build: have the
root Makefile generates the CFLAGS".

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>