cmake FLB_HAVE_ATTRIBUTE_ALLOC_SIZE examples

fluent/fluent-bit CMakeLists.txt :1043

check_c_source_compiles("
#include <stdlib.h>
__attribute__ ((alloc_size(1, 2))) static void* f(size_t a, size_t b) {
    return calloc(a, b);
}
int main() {
    f(1, 2);
    return 0;
}
" FLB_HAVE_ATTRIBUTE_ALLOC_SIZE)