[libc] Add dirent.h functions opendir, readdir, closedir and dirfd.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D130459
diff --git a/libc/src/CMakeLists.txt b/libc/src/CMakeLists.txt
index a53e382..19664ec 100644
--- a/libc/src/CMakeLists.txt
+++ b/libc/src/CMakeLists.txt
@@ -9,6 +9,7 @@
 add_subdirectory(stdlib)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
+  add_subdirectory(dirent)
   add_subdirectory(fcntl)
   add_subdirectory(pthread)
   add_subdirectory(sys)