BUILD: makefile: Update feature flags for OpenBSD

BUILD: makefile: Update feature flags for OpenBSD

Update the OpenBSD target features being enabled.

I updated the list of features after noticing
"BUILD: makefile: disable threads by default on OpenBSD".

The Makefile utilizing gcc(1) by default resulted in utilizing
our legacy and obsolete compiler (GCC 4.2.1) instead of the
proper system compiler (Clang), which does support TLS. With
"BUILD: makefile: change default value of CC from gcc to cc"
that is resolved.