v256_intrinsics_c.h: add missing stdbool.h include

Fixes Visual Studio build targeting Win32 after:
00f0b9689e v256_intrinsics_c.h: fix AVX2/C mismatch w/gcc+ubsan

Bug: 42302489
Change-Id: I6a020c24d666c1c913ca95777e44bda20d46b0b0

aom_dsp/simd/v256_intrinsics_c.h

diff --git a/aom_dsp/simd/v256_intrinsics_c.h b/aom_dsp/simd/v256_intrinsics_c.h
index fb096f8..cbcc1b0 100644
--- a/aom_dsp/simd/v256_intrinsics_c.h
+++ b/aom_dsp/simd/v256_intrinsics_c.h
@@ -12,6 +12,7 @@
 #ifndef AOM_AOM_DSP_SIMD_V256_INTRINSICS_C_H_
 #define AOM_AOM_DSP_SIMD_V256_INTRINSICS_C_H_
 
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>