fixup! golang: Expose Sema and Mutex as public Python and Cython/nogil API

_makesema declaration was giving a warning when compiling with C:

	In file included from golang/runtime/libgolang_test_c.c:26:
	./golang/libgolang.h:237:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
	 LIBGOLANG_API _sema *_makesema();
	 ^~~~~~~~~~~~~

Fix the prototype to be valid for both C and C++.
Fixes: 34b7a1f4.

golang/libgolang.h

@@ -234,7 +234,7 @@ extern LIBGOLANG_API const _selcase _default;
 // _sema corresponds to sync.Sema
 // no C-level analog is provided for sync.Mutex
 typedef struct _sema _sema;
-LIBGOLANG_API _sema *_makesema();
+LIBGOLANG_API _sema *_makesema(void);
 LIBGOLANG_API void _semafree(_sema *sema);
 LIBGOLANG_API void _semaacquire(_sema *sema);
 LIBGOLANG_API void _semarelease(_sema *sema);