Silence clang warnings under --enable-expensive-hardening, including:
+ implicit truncation of 64 bit values to 32 bit;
+ const char assignment to self;
+ tautological compare; and
+ additional parentheses around equality tests. (gcc uses these to
silence assignment, so clang warns when they're present in an
equality test. But we need to use extra parentheses in macros to
isolate them from other code).
There are as many divergent implementations of sys/queue.h as there
are operating systems shipping it, it would seem. They have some code
in common, but have drifted apart, and have added other stuff named
differently. So I'm taking a relatively sane one, and hoping for the
best.
I'm taking OpenBSD's in particular because of the lack of external
dependencies, the presence of a CIRCLEQ (we could use one of those in
places), and the liberal licensing terms.
I'm naming the file tor_queue.h, since historically we've run into
trouble having headers with the same names as system headers (log.h,
for example.)
