Deal with symbolic links for file and directories on Mac and Linux.

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 98d93e617ce6fc335b592a22f0d1b4d01b2e71ae..7f0806130ea5221dba1a9b59544088ba22d6fb40 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -141,7 +141,7 @@ File* File::OpenStdio(int fd) {
 bool File::Exists(const char* name) {
   struct stat st;
   if (TEMP_FAILURE_RETRY(stat(name, &st)) == 0) {
-    return S_ISREG(st.st_mode);  // Deal with symlinks?
+    return S_ISREG(st.st_mode);
   } else {
     return false;
   }