[libunwind] Disable DwarfFDECache if _LIBUNWIND_NO_HEAP=1

[kitaisreal]

In add method of DwarfFDECache we disable adding entries into cache if _LIBUNWIND_NO_HEAP=1. Other methods could also be disabled if _LIBUNWIND_NO_HEAP=1, to avoid mutex lock, unlock and empty cache check.

libunwind/src/UnwindCursor.hpp

 #ifdef __APPLE__
 template <typename A>
 bool DwarfFDECache<A>::_registeredForDyldUnloads = false;
 #endif
 
 template <typename A>
 typename A::pint_t DwarfFDECache<A>::findFDE(pint_t mh, pint_t pc) {
   pint_t result = 0;
+#if !defined(_LIBUNWIND_NO_HEAP)
   _LIBUNWIND_LOG_IF_FALSE(_lock.lock_shared());
   for (entry *p = _buffer; p < _bufferUsed; ++p) {
     if ((mh == p->mh) || (mh == kSearchAll)) {
       if ((p->ip_start <= pc) && (pc < p->ip_end)) {
         result = p->fde;
         break;
       }
     }
   }
   _LIBUNWIND_LOG_IF_FALSE(_lock.unlock_shared());
+#endif
   return result;
 }
 
 template <typename A>
 void DwarfFDECache<A>::add(pint_t mh, pint_t ip_start, pint_t ip_end,
                            pint_t fde) {
 #if !defined(_LIBUNWIND_NO_HEAP)
   _LIBUNWIND_LOG_IF_FALSE(_lock.lock());
#ifdef __APPLE__
   }
 #endif
   _LIBUNWIND_LOG_IF_FALSE(_lock.unlock());
 #endif
 }
 
 template <typename A>
 void DwarfFDECache<A>::removeAllIn(pint_t mh) {
+#if !defined(_LIBUNWIND_NO_HEAP)
   _LIBUNWIND_LOG_IF_FALSE(_lock.lock());
   entry *d = _buffer;
   for (const entry *s = _buffer; s < _bufferUsed; ++s) {
     if (s->mh != mh) {
       if (d != s)
         *d = *s;
       ++d;
     }
   }
   _bufferUsed = d;
   _LIBUNWIND_LOG_IF_FALSE(_lock.unlock());
+#endif
 }
 
 #ifdef __APPLE__
 template <typename A>
 void DwarfFDECache<A>::dyldUnloadHook(const struct mach_header *mh, intptr_t ) {
   removeAllIn((pint_t) mh);
 }
 #endif
 
 template <typename A>
 void DwarfFDECache<A>::iterateCacheEntries(void (*func)(
     unw_word_t ip_start, unw_word_t ip_end, unw_word_t fde, unw_word_t mh)) {
+#if !defined(_LIBUNWIND_NO_HEAP)
   _LIBUNWIND_LOG_IF_FALSE(_lock.lock());
   for (entry *p = _buffer; p < _bufferUsed; ++p) {
     (*func)(p->ip_start, p->ip_end, p->fde, p->mh);
   }
   _LIBUNWIND_LOG_IF_FALSE(_lock.unlock());
+#endif
 }
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 
 
 #define arrayoffsetof(type, index, field) ((size_t)(&((type *)0)[index].field))
 
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
 template <typename A> class UnwindSectionHeader {