[clang] [clang][x86] Add constexpr support for VNNI intrinsics (PR #190549)

[NagaChaitanya Vellanki via cfe-commits]

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@@ -24,6 +24,14 @@
                  __target__("avx512vl,avx512vnni"),                            \
                  __min_vector_width__(256)))
 
+#if defined(__cplusplus) && (__cplusplus >= 201103L)
+#define __DEFAULT_FN_ATTRS128_CONSTEXPR __DEFAULT_FN_ATTRS128 constexpr
----------------
chaitanyav wrote:

```
#if defined(__cplusplus) && (__cplusplus >= 201103L)
#define __DEFAULT_FN_ATTRS128                                                  \
  __attribute__((__always_inline__, __nodebug__,                               \
                 __target__("avx512vl,avx512vnni"),                            \
                 __min_vector_width__(128))) constexpr
#define __DEFAULT_FN_ATTRS256                                                  \
  __attribute__((__always_inline__, __nodebug__,                               \
                 __target__("avx512vl,avx512vnni"),                            \
                 __min_vector_width__(256))) constexpr
#else
#define __DEFAULT_FN_ATTRS128                                                  \
  __attribute__((__always_inline__, __nodebug__,                               \
                 __target__("avx512vl,avx512vnni"),                            \
                 __min_vector_width__(128)))
#define __DEFAULT_FN_ATTRS256                                                  \
  __attribute__((__always_inline__, __nodebug__,                               \
                 __target__("avx512vl,avx512vnni"),                            \
                 __min_vector_width__(256)))
#endif
```

https://github.com/llvm/llvm-project/pull/190549