mesa/main: Correct alloca() use without #include "c99_alloca.h"

Fixes: d231f95591 ("mesa: add hw select name stack code path")

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17073>

src/mesa/main/feedback.c

@@ -30,6 +30,7 @@
 
 
 #include "glheader.h"
+#include "c99_alloca.h"
 #include "context.h"
 #include "enums.h"
 #include "feedback.h"