[clang] [llvm] Allow Custom LTO Linking (PR #225492)

[Larry Meadows via llvm-commits]

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@@ -9891,6 +9891,28 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
         }
       }
 
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lfmeadow wrote:

I gather this came from downstream somewhere? It appears to be modifying LTO by looking for opt levels and adding them to a --lto-newpm-passes=default-post-link<O[312]> argument.
I have no idea what that argument does. At least, you need to find out when that downstream code was added and who did it. It would be really nice to have some tests. 

https://github.com/llvm/llvm-project/pull/225492