[clang] [Clang] Add __builtin_bswapg (PR #162433)

[via cfe-commits]

================
@@ -479,6 +479,14 @@ int h0 = __builtin_types_compatible_p(int, float);
 int h3 = __builtin_bswap16(0x1234) == 0x3412 ? 1 : f();
 int h4 = __builtin_bswap32(0x1234) == 0x34120000 ? 1 : f();
 int h5 = __builtin_bswap64(0x1234) == 0x3412000000000000 ? 1 : f();
+int h6 = __builtin_bswapg((char)(0x12)) == (char)(0x12) ? 1 : f();
+int h7 = __builtin_bswapg((short)(0x1234)) == (short)(0x3412) ? 1 : f();
+int h8 = __builtin_bswapg(0x00001234) == 0x34120000 ? 1 : f();
+int h9 = __builtin_bswapg(0x0000000000001234ULL) == 0x3412000000000000 ? 1 : f();
+float h10 = __builtin_bswapg(1.0f); // expected-error {{1st argument must be a scalar integer type (was 'float')}}
----------------
clingfei wrote:

Testing for arrays, pointers, enums, class, nullptr_t has been added. 
> What do we expect w/ charN_t, wchar_t, bool and int128_t types?

Currently __builtin_bswapg treats these types the same way as the corresponding byte integer types.


https://github.com/llvm/llvm-project/pull/162433