Add <experimental/coroutine>

This patch adds the library portions of the coroutines PDTS,
which should now be supported by Clang.

llvm-svn: 303836
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index c354cae..737ef9a 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -501,6 +501,10 @@
       header "experimental/chrono"
       export *
     }
+    module coroutine {
+      header "experimental/coroutine"
+      export *
+    }
     module deque {
       header "experimental/deque"
       export *