Add test_x86_avx512.cxx (GH #753)

TestPrograms/test_x86_avx512.cxx

@@ -0,0 +1,8 @@
+#include <cstdint>
+#include <immintrin.h>
+int main(int argc, char* argv[])
+{
+    uint64_t x[8] = {0};
+    __m512i y = _mm512_loadu_si512((__m512i*)x);
+    return 0;
+}