[analyzer] RunLoopAutoreleaseLeakChecker: Come up with a test for r348822.

Statement memoization was removed in r348822 because it was noticed to cause
memory corruption. This was happening because a reference to an object
in a DenseMap was used after being invalidated by inserting a new key
into the map.

This test case crashes reliably under ASan (i.e., when Clang is built with
-DLLVM_USE_SANITIZER="Address") on at least some machines before r348822
and doesn't crash after it.

llvm-svn: 349000