[lld] Fix lld crash wrt generated thunks growing away from the patched code (PR #170495)

[Peter Smith via llvm-commits]

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@@ -390,7 +390,7 @@ class elf::Patch843419Section final : public SyntheticSection {
   Symbol *patchSym;
 };
 
-Patch843419Section::Patch843419Section(Ctx &ctx, InputSection *p, uint64_t off)
+Patch843419Section::Patch843419Section(Ctx &ctx, InputSection *p, uint64_t off, Symbol* patcheeCodeSym)
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smithp35 wrote:

It looks like we start with a `Defined*` then use a `Symbol*` parameter then dyn_cast back to Defined* below. 

If we use Defined* for the parameter can we avoid the dyn_cast?

https://github.com/llvm/llvm-project/pull/170495