Fix support for BSD operating systems

Close issue #230

src/internal/formatdetect.cpp

@@ -343,7 +343,9 @@ struct OffsetSignature {
 #elif defined(__GNUC__) || defined(__clang__)
 //Note: the versions of gcc and clang that can compile bit7z should also have this builtin, hence there is no need
 //      for checking the compiler version or using the _has_builtin macro.
+#ifndef bswap64
 #define bswap64 __builtin_bswap64
+#endif
 #else
 static inline uint64_t bswap64( uint64_t x ) {
     return  ((x << 56) & 0xff00000000000000ULL) |

src/internal/fsutil.cpp

@@ -179,7 +179,8 @@ static const mode_t global_umask = []() noexcept -> mode_t {
 #endif
 
 #ifndef _WIN32
-#ifdef __APPLE__
+#if defined( __APPLE__ ) || defined( BSD ) || \
+    defined( __FreeBSD__ ) || defined( __NetBSD__ ) || defined( __OpenBSD__ ) || defined( __DragonFly__ )
 using stat_t = struct stat;
 const auto os_lstat = &lstat;
 const auto os_stat = &stat;