[clang] [Multilib] Extend the Multilib system to support an IncludeDirs field. (PR #146651)

[Petr Hosek via cfe-commits]

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@@ -501,6 +511,16 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
         addSystemInclude(DriverArgs, CC1Args, TargetDir.str());
         break;
       }
+      if (!M.includeDirs().empty()) {
+        // Add include directories specified in multilib.yaml under the
+        // 'IncludeDirs' field
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petrhosek wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/146651