[clang] [Driver] Find vendor-prefixed musl GCC toolchains (PR #206477)

[Adeel Mujahid via cfe-commits]

================
@@ -344,7 +344,7 @@ Non-comprehensive list of changes in this release
 - Updated support for Unicode from 15.1 to 18.0.
 
 - Linux and Windows toolchains now support Clang multilibs using
-  ``-fmultilib-flag=``.
+``-fmultilib-flag=``.
----------------
am11 wrote:

```suggestion
  ``-fmultilib-flag=``.
```

https://github.com/llvm/llvm-project/pull/206477