Use abort() for fallback implementations of unreachable().
diff --git a/include/jemalloc/internal/util.h b/include/jemalloc/internal/util.h
index 6e21470..228584a 100644
--- a/include/jemalloc/internal/util.h
+++ b/include/jemalloc/internal/util.h
@@ -73,12 +73,12 @@
JEMALLOC_CLANG_HAS_BUILTIN(__builtin_unreachable)
# define unreachable() __builtin_unreachable()
# else
-# define unreachable()
+# define unreachable() abort()
# endif
#else
# define likely(x) !!(x)
# define unlikely(x) !!(x)
-# define unreachable()
+# define unreachable() abort()
#endif
#include "jemalloc/internal/assert.h"