First part of P0600 - '[[nodiscard] in the standard library'. Mark the 'empty()' methods of all the containers as nodiscard. If you're calling empty() w/o looking at the result, you probably meanto to call 'clear()'. c++2a only

llvm-svn: 318269
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 72c8fad4270a9810e7868892910b8029e8a92b1c
diff --git a/include/array b/include/array
index 1278099..4eb2fe6 100644
--- a/include/array
+++ b/include/array
@@ -183,7 +183,7 @@
     _LIBCPP_CONSTEXPR size_type size() const _NOEXCEPT {return _Size;}
     _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR size_type max_size() const _NOEXCEPT {return _Size;}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR bool empty() const _NOEXCEPT {return _Size == 0;}
 
     // element access: