[gold] Remove inconsistent llvm_unreachable()

[davide]

Summary

message(LDPL_FATAL, ...) should never return. This is the only place in the gold-plugin code where we put an unreachable() after that to ensure the invariant is satisfied. I think that we can either add llvm_unreachable() after each use of LDPL_FATAL in the source file, or remove this one.
I just don't like the inconsistency, so I vote for the removal.

[• rafael]

It might be there to avoid a warning.

LGTM if no warnings with GCC or clang.

Cheers,
Rafael

tools/gold/gold-plugin.cpp

std::string ErrStorage;
     DiagnosticPrinterRawOStream DP(OS);
     DI.print(DP);
   }
   ld_plugin_level Level;
   switch (DI.getSeverity()) {
   case DS_Error:
     message(LDPL_FATAL, "LLVM gold plugin has failed to create LTO module: %s",
             ErrStorage.c_str());
-    llvm_unreachable("Fatal doesn't return.");
   case DS_Warning:
     Level = LDPL_WARNING;
     break;
   case DS_Note:
   case DS_Remark:
     Level = LDPL_INFO;
     break;
   }