[clang] [clang]: baremetal `multilib.yaml` discovery (PR #227965)

[Mythreya Kuricheti via cfe-commits]

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@@ -202,10 +202,10 @@ ToolChain::findMultilibsYAML(const llvm::opt::ArgList &Args, const Driver &D,
   }
 
   SmallString<128> MultilibPath;
-  if (!FallbackDir.empty())
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MythreyaK wrote:

The single `multilib.yaml` behavior isn't impacted with this change (existing setups should work identically). This change just makes the per-triple file work too if specified, like the hosted musl setups. 

Thank you for the context on the Qualcomm setup and your time in reviewing this! I'll switch to a single `multilib.yaml`. Happy to close this PR if the support for per-triple yaml is unnecessary!

https://github.com/llvm/llvm-project/pull/227965