Add provisions for windows support for BF16 code including CMake provision for enabling AVX512_BF16 (llama/7258)

ggml-impl.h

@@ -17,6 +17,18 @@
 #define MIN(a, b) ((a) < (b) ? (a) : (b))
 #define MAX(a, b) ((a) > (b) ? (a) : (b))
 
+#if defined(_WIN32)
+
+#define m512bh(p) p
+#define m512i(p) p
+
+#else
+
+#define m512bh(p) (__m512bh)(p)
+#define m512i(p) (__m512i)(p)
+
+#endif
+
 /**
  * Converts brain16 to float32.
  *