Merging r367906:

------------------------------------------------------------------------
r367906 | jkorous | 2019-08-05 20:44:07 +0200 (Mon, 05 Aug 2019) | 5 lines

[DirectoryWatcher][linux] Fix build for older kernels

Apparently kernel support for IN_EXCL_UNLINK in inotify_add_watch() doesn't imply it's defined in sys/inotify.h.

https://bugs.llvm.org/show_bug.cgi?id=42824
------------------------------------------------------------------------

llvm-svn: 367995