swrast: Fix implicit declaration warnings

In a recent commit,
    commit 1c0f1dd42a50464eeb81de4aad8eecf24b3d6c89
    Author: Chad Versace <chad.versace@linux.intel.com>
    swrast: Fix fixed-function fragment processing
I defined a new function,_swrast_fragment_program, but neglected
to #include s_fragprog.h for clients of that function.

Note: This is a candidate for the 8.0 branch.
Reported-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
diff --git a/src/mesa/swrast/s_context.h b/src/mesa/swrast/s_context.h
index ae239a9..363bdf0 100644
--- a/src/mesa/swrast/s_context.h
+++ b/src/mesa/swrast/s_context.h
@@ -47,6 +47,7 @@
 #include "main/mtypes.h"
 #include "program/prog_execute.h"
 #include "swrast.h"
+#include "s_fragprog.h"
 #include "s_span.h"