Add an IR test adhering the suggestion of the reviewer

Author: Camsyn

llvm/test/Instrumentation/ThreadSanitizer/capture.ll

@@ -47,6 +47,21 @@ entry:
 ; CHECK: __tsan_write
 ; CHECK: ret void
 
+define void @captured3() nounwind uwtable sanitize_thread {
+entry:
+  %stkobj = alloca [2 x i32], align 8
+  ; escapes due to store into global
+  store ptr %stkobj, ptr @sink, align 8
+  ; derived is captured as its base object is captured
+  %derived = getelementptr inbounds i32, ptr %stkobj, i64 1
+  store i32 42, ptr %derived, align 4
+  ret void
+}
+; CHECK-LABEL: define void @captured3
+; CHECK: __tsan_write
+; CHECK: __tsan_write
+; CHECK: ret void
+
 define void @notcaptured0() nounwind uwtable sanitize_thread {
 entry:
   %ptr = alloca i32, align 4