nir: Add missing #include for c99_alloca.h

Fixes: 3dd9a978 ("nir: add new pass nir_lower_io_indirect_loads")
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36940>

src/compiler/nir/nir_lower_io_indirect_loads.c

@@ -23,6 +23,7 @@
 
 #include "nir.h"
 #include "nir_builder.h"
+#include <c99_alloca.h>
 
 typedef struct {
    nir_variable *var[INTERP_MODE_COUNT];