Fix failing LLVM ArrayRef unit test (#4800)

The initializer list goes out of scope after the expression it is used
in, so the ArrayRef points to invalid memory. This change keeps the
initialization list around so that the array ref remains valid through
the test.

Author: llvm-beanz

unittests/ADT/ArrayRefTest.cpp

@@ -99,7 +99,8 @@ static void ArgTest12(ArrayRef<int> A) {
 }
 
 TEST(ArrayRefTest, InitializerList) {
-  ArrayRef<int> A = { 0, 1, 2, 3, 4 };
+  std::initializer_list<int> InitList = { 0, 1, 2, 3, 4 };
+  ArrayRef<int> A = InitList;
   for (int i = 0; i < 5; ++i)
     EXPECT_EQ(i, A[i]);