As mentioned at
https://gcc.gnu.org/ml/gcc-patches/2015-08/msg00251.html

some assemblers don't support -mcpu=thunderx, so the dg-do assemble test will FAIL.
Mark this test as compile-only as assembling it is not essential to the functionality it tests.

Committed as obvious with r226886.

2015-08-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * gcc.target/aarch64/target_attr_1.c: Make test compile-only.