https://gitlab.freedesktop.org/xorg/driver/xf86-video-intel/-/issues/230
See also https://www.illumos.org/issues/1777

--- xf86-video-intel-e6a4c4740c15ace9dd79dc7c18955f2eb413a6a5/src/sna/sna_video.c.orig
+++ xf86-video-intel-e6a4c4740c15ace9dd79dc7c18955f2eb413a6a5/src/sna/sna_video.c
@@ -67,6 +67,9 @@
 #else
 #define bswap_32 bswap32
 #endif
+#elif defined(__illumos__)
+#include <sys/byteorder.h>
+#define bswap_32 BSWAP_32
 #else
 #include <byteswap.h>
 #endif