Index: lrzip_private.h
--- lrzip_private.h.orig
+++ lrzip_private.h
@@ -46,8 +46,6 @@
 
 #ifdef HAVE_ALLOCA_H
 # include <alloca.h>
-#elif defined __GNUC__
-# define alloca __builtin_alloca
 #elif defined _AIX
 # define alloca __alloca
 #elif defined _MSC_VER
@@ -144,7 +142,7 @@ extern int errno;
 #define unlikely(x)	__builtin_expect(!!(x), 0)
 #define __maybe_unused	__attribute__((unused))
 
-#if defined(__MINGW32__) || defined(__CYGWIN__) || defined(__ANDROID__) || defined(__APPLE__)
+#if defined(__MINGW32__) || defined(__CYGWIN__) || defined(__ANDROID__) || defined(__APPLE__) || defined(__OpenBSD__)
 # define ffsll __builtin_ffsll
 #endif