For aarch64, ICache::invalidate_word/range contain calls to the undeclared function __clear_cache. This works when using -std=gnu++<whatever>, but not when using -std=c++<whatever>.

This works today because we are using -std=gnu++98. However, when providing C++14 support (JDK-8208089) the plan is to use -std=c++14 and not enable gnu extensions. That call to __clear_cache is the only place that currently requires gnu extensions. It would be undesirable to enable gnu extensions in shared code just to allow this one use platform-specific code.

This can be solved by using __builtin___clear_cache instead of calling __clear_cache directly.