Add test case

tests/ui/crashes/auxiliary/ice-7868-aux.rs

@@ -0,0 +1,3 @@
+fn zero() {
+    unsafe { 0 };
+}

tests/ui/crashes/ice-7868.rs

@@ -0,0 +1,6 @@
+#![warn(clippy::undocumented_unsafe_blocks)]
+
+#[path = "auxiliary/ice-7868-aux.rs"]
+mod zero;
+
+fn main() {}