[clang] [WebAssembly] Enable musttail only when tail-call is enabled (PR #163618)

[Aaron Ballman via cfe-commits]

================
@@ -546,6 +546,8 @@ NetBSD Support
 WebAssembly Support
 ^^^^^^^^^^^^^^^^^^^
 
+- Fix a bug so that __has_attribute(musttail) should not be true anymore when notail is not enabled.
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AaronBallman wrote:

```suggestion
- Fix a bug so that ``__has_attribute(musttail)`` is no longer true when notail is not enabled. (#GH163256)
```

https://github.com/llvm/llvm-project/pull/163618