Fix _libdispatch_tsd_cleanup signature.

[triplef]

Fixes the following error when building for Windows x86:

..\src\queue.c(7376,1): error: function declared 'stdcall' here was previously declared without calling convention
_libdispatch_tsd_cleanup(void *ctx)
^
..\src/shims/tsd.h(161,13): note: previous declaration is here
extern void _libdispatch_tsd_cleanup(void *ctx);

DISPATCH_TSD_DTOR_CC is part of the _libdispatch_tsd_cleanup signature in queue.c, but not in the external declaration in tsd.h. DISPATCH_TSD_DTOR_CC resolves to __stdcall on Windows.

[AZero13]

@etcwilde we can close this since this was merged already

[triplef]

Yup, this was done in #569.