swrast: Build fix for Solaris

Fixes regression from commit 5b2d3480f57168d50ad24cf0b8c9244414bd3701

Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>
diff --git a/configure.ac b/configure.ac
index 095e23e..5594548 100644
--- a/configure.ac
+++ b/configure.ac
@@ -649,6 +649,7 @@
 fi
 
 AC_CHECK_HEADER([xlocale.h], [DEFINES="$DEFINES -DHAVE_XLOCALE_H"])
+AC_CHECK_HEADER([sys/sysctl.h], [DEFINES="$DEFINES -DHAVE_SYS_SYSCTL_H"])
 AC_CHECK_FUNC([strtof], [DEFINES="$DEFINES -DHAVE_STRTOF"])
 
 dnl Check to see if dlopen is in default libraries (like Solaris, which