[clang] [clang] Add `__bf16` Type Support Macros With Literal Suffix Support (PR #134214)

[via cfe-commits]

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overmighty wrote:

You could have multiple `// RUN:` lines with different targets and macro definitions. For example:

```cpp
// RUN: %clang_cc1 -fsyntax-only -verify -pedantic -triple x86_64 -DSUPPORTED %s
// RUN: %clang_cc1 -fsyntax-only -verify -pedantic -triple armv7 %s
// RUN: %clang_cc1 -fsyntax-only -verify -pedantic -triple armv7 -target-feature +bf16 -DSUPPORTED %s
```

Then you can guard the test cases with `#ifdef SUPPORTED`/`#ifndef SUPPORTED`.

Also, the test will currently fail if testing a Clang build with a default target triple that doesn't support bfloat16.

https://github.com/llvm/llvm-project/pull/134214