Work around clang-tidy and clang-check powers.

clang-tidy is less powerful so needs some help. clang-check is much
cleverer so we have to let it know that we're dumbing down for
clang-tidy.

Change-Id: I84a5e92da360b6f367d8b4f31e533b168aea2c5d
diff --git a/src/api.c b/src/api.c
index 1d44691..b2e2c36 100644
--- a/src/api.c
+++ b/src/api.c
@@ -303,10 +303,13 @@
 		/*
 		 * clang-tidy isn't able to prove that
 		 * `from->id != HF_PRIMARY_VM_ID` so cover that specific case
-		 * explicitly so as not to hide other possible bugs.
+		 * explicitly so as not to hide other possible bugs. clang-check
+		 * is more clever and finds that this is dead code so we also
+		 * pretend to use the new value.
 		 */
 		if (from->id == HF_PRIMARY_VM_ID) {
 			vcpu = 0;
+			(void)vcpu;
 		}
 		goto out;
 	}