8273153: Consolidate file_exists into os:file_exists

Reviewed-by: iklam, ccheung

src/hotspot/share/runtime/os.cpp

@@ -1395,6 +1395,14 @@ bool os::set_boot_path(char fileSep, char pathSep) {
   return false;
 }
 
+bool os::file_exists(const char* filename) {
+  struct stat statbuf;
+  if (filename == NULL || strlen(filename) == 0) {
+    return false;
+  }
+  return os::stat(filename, &statbuf) == 0;
+}
+
 // Splits a path, based on its separator, the number of
 // elements is returned back in "elements".
 // file_name_length is used as a modifier for each path's