sna: Add include <alloca.h> for compiling on Solaris

Reported-by: Richard Palo <richard@netbsd.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89762
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

configure.ac

@@ -416,7 +416,7 @@ AC_ARG_ENABLE(sna,
 	      [SNA="$enableval"],
 	      [SNA=auto])
 
-AC_CHECK_HEADERS([dev/wscons/wsconsio.h])
+AC_CHECK_HEADERS([dev/wscons/wsconsio.h alloca.h])
 
 if test "x$SNA" != "xno"; then
 	AC_DEFINE(USE_SNA, 1, [Enable SNA support])

src/sna/sna_display.c

@@ -40,6 +40,10 @@
 #include <poll.h>
 #include <ctype.h>
 
+#if HAVE_ALLOCA_H
+#include <alloca.h>
+#endif
+
 #include "sna.h"
 #include "sna_reg.h"
 #include "fb/fbpict.h"