Merge commit '6419f1c78014' from apple/stable/20200108 into swift/release/5.3

git apple-llvm automerger · git apple-llvm automerger · commit 88e2e2085421 · 2020-06-09T15:57:09.000-07:00
diff --git a/clang-tools-extra/clangd/Shutdown.cpp b/clang-tools-extra/clangd/Shutdown.cpp
@@ -10,6 +10,7 @@
 
 #include <atomic>
 #include <thread>
+#include <cstdlib>
 
 namespace clang {
 namespace clangd {
