[libcxx] [test] Strip trailing whitespace, NFC.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324959 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/algorithms/alg.modifying.operations/alg.rotate/rotate_copy.pass.cpp

@@ -23,11 +23,11 @@
 // TEST_CONSTEXPR bool test_constexpr() {
 //     int ia[] = {1, 3, 5, 2, 5, 6};
 //     int ib[std::size(ia)] = {0};
-//     
+//
 //     const size_t N = 2;
 //     const auto middle = std::begin(ia) + N;
 //     auto it = std::rotate_copy(std::begin(ia), middle, std::end(ia), std::begin(ib));
-// 
+//
 //     return std::distance(std::begin(ib), it) == std::size(ia)
 //         && std::equal   (std::begin(ia), middle,       std::begin(ib) + std::size(ia) - N)
 //         && std::equal   (middle,         std::end(ia), std::begin(ib))