Fix the -DTHREADSAFE=OFF build

[lhchavez]

This change avoids using the (void)0 construct for some of the mutex
#defines, since that makes the "return type" of those "functions" to
be void instead of int.

[lhchavez]

oops!

[ethomson]

It should be returning an int? Is there a platform where it's not?

our win32 function returns an int

posix is just a define for pthread which returns an int

and the no-thread version should be 0

[lhchavez]

It should be returning an int? Is there a platform where it's not?

[...]

and the no-thread version should be 0

the no-thread version! that's a void, not an int. i think the solution is to avoid using the (void)0 construct and instead use a real inline function that returns 0.

[ethomson]

the no-thread version! that's a void, not an int. i think the solution is to avoid using the (void)0 construct and instead use a real inline function that returns 0.

ah so it is. i focused on the 0 and didn't think about the cast in front of it. i think an inline function that returns 0 makes sense. certainly it's easier to reason about than what's there. 😢

[lhchavez]

couldn't think of a better name. also, lmk if we need to do something clever to explicitly mark the arguments as unused (right now it's a non-issue on my machine).

[ethomson]

Thanks for this!