compat UPDATE find byteswap correctly

Author: Roytak

CMakeModules/UseCompat.cmake

@@ -61,6 +61,8 @@ macro(USE_COMPAT)
 
     check_include_file("alloca.h" HAVE_ALLOCA_H)
 
+    check_include_file("byteswap.h" HAVE_BYTESWAP_H)
+
     list(REMOVE_ITEM CMAKE_REQUIRED_DEFINITIONS -D_POSIX_C_SOURCE=200809L)
     list(REMOVE_ITEM CMAKE_REQUIRED_DEFINITIONS -D_GNU_SOURCE)
     list(REMOVE_ITEM CMAKE_REQUIRED_DEFINITIONS -D__BSD_VISIBLE=1)

compat/compat.h.in

@@ -26,11 +26,12 @@
 # include <alloca.h>
 #endif
 
-#if defined (__APPLE__) || defined (_WIN32)
+#cmakedefine HAVE_BYTESWAP_H
+#ifdef HAVE_BYTESWAP_H
+# include <byteswap.h>
+#else
 # define bswap_32 __builtin_bswap32
 # define bswap64 __builtin_bswap64
-#else
-# include <byteswap.h>
 #endif
 
 #include <limits.h>