Ondřej Surý authored Dec 02, 2019 and Ondřej Surý committed Dec 03, 2019

The new ISC_THREAD_LOCAL macro unifies usage of platform dependent
Thread Local Storage definition thread_local vs __thread vs
__declspec(thread) to a single macro.

The commit also unifies the required level of support for TLS as for
some parts of the code it was mandatory and for some parts of the code
it wasn't.