[HWASan] Fix brittle stack-oob.c test.

Author: morehouse

compiler-rt/test/hwasan/TestCases/stack-oob.c

@@ -25,7 +25,7 @@ int f() {
 int main() {
   f();
   // CHECK: READ of size 1 at
-  // CHECK: #0 {{.*}} in f{{.*}}stack-oob.c:19
+  // CHECK: #0 {{.*}} in f{{.*}}stack-oob.c:[[@LINE-6]]
 
   // CHECK: is located in stack of threa