Add test to self-check needs-target-has-atomic directive

Author: kei519

tests/ui/compiletest-self-test/only-target-has-atomic.rs

@@ -0,0 +1,9 @@
+// Check this ignored because x86_64-unknown-linux-gnu does not have 128-bit atomic operation.
+
+//@ only-x86_64-unknown-linux-gnu
+//@ needs-target-has-atomic: 128
+
+fn main() {
+    #[cfg(not(target_has_atomic = "128"))]
+    compile_error!("target does not have 128-bit atomic operation");
+}