Replace llvm::integer_sequence and friends with the C++14 standard version

The implementation in libc++ takes O(1) compile time, ours was O(n).

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@368990 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/clangd/Function.h b/clangd/Function.h
index 6d91136..91aaa48 100644
--- a/clangd/Function.h
+++ b/clangd/Function.h
@@ -59,14 +59,14 @@
 public:
   template <class... RestArgs>
   auto operator()(RestArgs &&... Rest)
-      -> decltype(this->CallImpl(llvm::index_sequence_for<Args...>(),
+      -> decltype(this->CallImpl(std::index_sequence_for<Args...>(),
                                  std::forward<RestArgs>(Rest)...)) {
 
 #ifndef NDEBUG
     assert(!WasCalled && "Can only call result of Bind once.");
     WasCalled = true;
 #endif
-    return CallImpl(llvm::index_sequence_for<Args...>(),
+    return CallImpl(std::index_sequence_for<Args...>(),
                     std::forward<RestArgs>(Rest)...);
   }
 };
diff --git a/clangd/unittests/Matchers.h b/clangd/unittests/Matchers.h
index 0946398..d477cf7 100644
--- a/clangd/unittests/Matchers.h
+++ b/clangd/unittests/Matchers.h
@@ -89,12 +89,12 @@
 
   template <typename T> operator Matcher<const std::vector<T> &>() const {
     return ::testing::MakeMatcher(new SubsequenceMatcher<T>(
-        TypedMatchers<T>(llvm::index_sequence_for<M...>{})));
+        TypedMatchers<T>(std::index_sequence_for<M...>{})));
   }
 
 private:
   template <typename T, size_t... I>
-  std::vector<Matcher<T>> TypedMatchers(llvm::index_sequence<I...>) const {
+  std::vector<Matcher<T>> TypedMatchers(std::index_sequence<I...>) const {
     return {std::get<I>(Matchers)...};
   }
 };