Приложение сыпет в лог такими строчками
... with incorrect signature.  Method has ...

файл sendmsg2.c

#ifndef NO_SELECTOR_MISMATCH_WARNINGS
static struct objc_slot* objc_selector_type_mismatch(Class cls, SEL
                selector, Slot_t result)
{
        fprintf(stderr, "Calling [%s %c%s] with incorrect signature.  "
                        "Method has %s, selector has %s\n",
                        cls->name,
                        class_isMetaClass(cls) ? '+' : '-',
                        sel_getName(selector),
                        result->types,
                        sel_getType_np(selector));
        return result;
}
#else
static struct objc_slot* objc_selector_type_mismatch(Class cls, SEL
                selector, Slot_t result)
{
        return result;
}
#endif

CMakeLists.txt

# For release builds, we disable spamming the terminal with warnings about
# selector type mismatches
if (CMAKE_BUILD_TYPE STREQUAL Release)
        add_definitions(-DNO_SELECTOR_MISMATCH_WARNINGS)
else ()
        add_definitions(-DGC_DEBUG)
endif ()

собрал с таким изменением spec файла

cmake \
%ifarch x86_64
        -DLIB_SUFFIX:STRING=64 \
%endif
        -DCMAKE_BUILD_TYPE=Release \
...

лог файл больше не засоряется.