Fix directory existence query error

runtime/bin/directory_macos.cc

Index: runtime/bin/directory_macos.cc
diff --git a/runtime/bin/directory_macos.cc b/runtime/bin/directory_macos.cc
index b24b9c8d4b4b4d93a86c5d4d15ad4d66d0ba4ea7..ca0d41bb1449723a0fadbcf845ae61872b1c5dc3 100644
--- a/runtime/bin/directory_macos.cc
+++ b/runtime/bin/directory_macos.cc
@@ -351,6 +351,9 @@ Directory::ExistsResult Directory::Exists(const char* dir_name) {
     if (S_ISDIR(entry_info.st_mode)) {
       return EXISTS;
     } else {
+      // An OSError may be constructed based on the return value of this
+      // function, so set errno to something that makes sense.
+      errno = ENOTDIR;
       return DOES_NOT_EXIST;
     }
   } else {