Re-apply "[libcxx] implement <simd> ABI for Clang/GCC vector extension, constructors, copy_from and copy_to."

...with proper guarding #ifdefs for unsupported C++11.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@338318 91177308-0d34-0410-b5e6-96231b3b80d8

Author: timshen91

include/__config

@@ -620,6 +620,8 @@ namespace std {
 
 #define _LIBCPP_ALWAYS_INLINE __forceinline
 
+#define _LIBCPP_HAS_NO_VECTOR_EXTENSION
+
 #elif defined(_LIBCPP_COMPILER_IBM)
 
 #define _ALIGNAS(x) __attribute__((__aligned__(x)))
@@ -652,6 +654,8 @@ namespace std {
 
 #define _LIBCPP_ALWAYS_INLINE __attribute__ ((__always_inline__))
 
+#define _LIBCPP_HAS_NO_VECTOR_EXTENSION
+
 #endif // _LIBCPP_COMPILER_[CLANG|GCC|MSVC|IBM]
 
 #if _LIBCPP_STD_VER >= 17

include/experimental/__config

@@ -64,4 +64,11 @@
 #define _LIBCPP_END_NAMESPACE_EXPERIMENTAL_SIMD_ABI \
     } _LIBCPP_END_NAMESPACE_EXPERIMENTAL_SIMD
 
+// TODO: support more targets
+#if defined(__AVX__)
+#define _LIBCPP_NATIVE_SIMD_WIDTH_IN_BYTES 32
+#else
+#define _LIBCPP_NATIVE_SIMD_WIDTH_IN_BYTES 16
+#endif
+
 #endif