Fix directory existence query error

runtime/bin/directory_fuchsia.cc

Index: runtime/bin/directory_fuchsia.cc
diff --git a/runtime/bin/directory_fuchsia.cc b/runtime/bin/directory_fuchsia.cc
index 94a86d1618f342a1a47472557b90fe0c1cfcf1a6..7fdf20529a1f98bcd5df71ea3ad73eec86487192 100644
--- a/runtime/bin/directory_fuchsia.cc
+++ b/runtime/bin/directory_fuchsia.cc
@@ -249,6 +249,9 @@ 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 = ENOENT;
       return DOES_NOT_EXIST;
     }
   } else {