#define __STRMERGE(a, b) a##b
#define _STRMERGE(a, b) __STRMERGE(a, b)

#ifdef __clang__
static void __attribute__ ((unused)) __clang_cleanup_func(void (^*dfunc) (void))
{
    (*dfunc) ();
}

#define defer void (^_STRMERGE(__defer_f_, __COUNTER__))(void) __attribute__((cleanup(__clang_cleanup_func))) __attribute__((unused)) = ^
#else
#define __block
#define _DEFER(a, count) \
    auto void _STRMERGE(__defer_f_, count)(void *_defer_arg __attribute__((unused))); \
    int _STRMERGE(__defer_var_, count) __attribute__((cleanup(_STRMERGE(__defer_f_, count)))) __attribute__((unused)); \
    void _STRMERGE(__defer_f_, count)(void *_defer_arg __attribute__((unused)))
#define defer _DEFER(a, __COUNTER__)
#endif


===
Clang compilation:
clang -fblocks -lBlocksRuntime

GCC compilation:
gcc -std=c11
===
Example:

void func(void) {
  void *a = malloc(10);
  defer { free(a); }
  do..sth..
  return;
}