[lld] [llvm] Re-apply "[NFCI][LTO][lld] Optimize away symbol copies within LTO global resolution in ELF" (PR #107792)

[Teresa Johnson via llvm-commits]

================
@@ -1797,18 +1799,18 @@ void BitcodeFile::parse() {
 void BitcodeFile::parseLazy() {
   numSymbols = obj->symbols().size();
   symbols = std::make_unique<Symbol *[]>(numSymbols);
-  for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
+  for (auto [i, irSym] : llvm::enumerate(obj->symbols())) {
+    // Keep copies of per-module undefined symbols for LTO::GlobalResolutions
----------------
teresajohnson wrote:

Maybe update the comment a bit since it only talks about undefined symbols but now applies to both. Probably pull up the other comment below on line 1806 and combine them?

https://github.com/llvm/llvm-project/pull/107792