tcg/i386: Add have_atomic16

Notice when Intel or AMD have guaranteed that vmovdqa is atomic.
The new variable will also be used in generated code.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/qemu/cpuid.h

@@ -71,6 +71,24 @@
 #define bit_LZCNT       (1 << 5)
 #endif
 
+/*
+ * Signatures for different CPU implementations as returned from Leaf 0.
+ */
+
+#ifndef signature_INTEL_ecx
+/* "Genu" "ineI" "ntel" */
+#define signature_INTEL_ebx     0x756e6547
+#define signature_INTEL_edx     0x49656e69
+#define signature_INTEL_ecx     0x6c65746e
+#endif
+
+#ifndef signature_AMD_ecx
+/* "Auth" "enti" "cAMD" */
+#define signature_AMD_ebx       0x68747541
+#define signature_AMD_edx       0x69746e65
+#define signature_AMD_ecx       0x444d4163
+#endif
+
 static inline unsigned xgetbv_low(unsigned c)
 {
     unsigned a, d;