Fix libfuzzer detection and shared object symbols issues

Don't export __throw_length_error, and don't import abort

ConflictSet.cpp

@@ -152,7 +152,7 @@ template <class T> struct ArenaAlloc {
 
   [[nodiscard]] T *allocate(size_t n) {
     if (n > 0xfffffffffffffffful / sizeof(T)) { // NOLINT
-      abort();
+      __builtin_unreachable();
     }
 
     return static_cast<T *>((void *)new (std::align_val_t(alignof(T)), *arena)
@@ -1136,7 +1136,7 @@ __attribute__((__visibility__("default"))) void ConflictSet_destroy(void *cs) {
 }
 
 namespace std {
-void __throw_length_error(const char *) { abort(); }
+void __throw_length_error(const char *) { __builtin_unreachable(); }
 } // namespace std
 
 namespace {