Fix directory existence query error

runtime/bin/directory_linux.cc

Index: runtime/bin/directory_linux.cc
diff --git a/runtime/bin/directory_linux.cc b/runtime/bin/directory_linux.cc
index 357a580e00681af00d9011600935feefc96c31f8..f2a064aeca8c8e8c452c920a969f4b23bf3c9f2e 100644
--- a/runtime/bin/directory_linux.cc
+++ b/runtime/bin/directory_linux.cc
@@ -360,6 +360,9 @@ 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 {