Add compile-fail test

Author: jonas-schievink

cortex-m-rt/tests/compile-fail/exception-v8only.rs

@@ -0,0 +1,16 @@
+#![no_main]
+#![no_std]
+
+extern crate cortex_m_rt;
+extern crate panic_halt;
+
+use cortex_m_rt::{entry, exception};
+
+#[entry]
+fn foo() -> ! {
+    loop {}
+}
+
+#[exception]
+fn SecureFault() {}
+//~^ ERROR no variant or associated item named `SecureFault`