[DRAFT] "Builtins world" for LTO

[mysterymath]

A crummy draft patch to demonstrate how LTO can be altered to treat builtin libfuncs with more respect after LTO symbol resolution

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff origin/main HEAD --extensions h,cpp -- lld/ELF/Driver.cpp lld/ELF/LTO.cpp lld/ELF/LTO.h llvm/include/llvm/LTO/LTO.h llvm/include/llvm/LTO/LTOBackend.h llvm/lib/LTO/LTO.cpp llvm/lib/LTO/LTOBackend.cpp llvm/lib/LTO/LTOCodeGenerator.cpp llvm/lib/Object/IRSymtab.cpp --diff_from_common_commit

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changing origin/main to the base branch/commit you want to compare against.
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View the diff from clang-format here.

diff --git a/llvm/include/llvm/LTO/LTO.h b/llvm/include/llvm/LTO/LTO.h
index d0a447df6..f128193f9 100644
--- a/llvm/include/llvm/LTO/LTO.h
+++ b/llvm/include/llvm/LTO/LTO.h
@@ -402,7 +402,8 @@ public:
   LLVM_ABI Error add(std::unique_ptr<InputFile> Obj,
                      ArrayRef<SymbolResolution> Res);
 
-  LLVM_ABI void setBitcodeLibFuncs(const SmallVector<const char *> &BitcodeLibFuncs);
+  LLVM_ABI void
+  setBitcodeLibFuncs(const SmallVector<const char *> &BitcodeLibFuncs);
 
   /// Returns an upper bound on the number of tasks that the client may expect.
   /// This may only be called after all IR object files have been added. For a
diff --git a/llvm/include/llvm/LTO/LTOBackend.h b/llvm/include/llvm/LTO/LTOBackend.h
index 26bff2281..2e5334740 100644
--- a/llvm/include/llvm/LTO/LTOBackend.h
+++ b/llvm/include/llvm/LTO/LTOBackend.h
@@ -40,7 +40,7 @@ LLVM_ABI bool opt(const Config &Conf, TargetMachine *TM, unsigned Task,
                   ModuleSummaryIndex *ExportSummary,
                   const ModuleSummaryIndex *ImportSummary,
                   const std::vector<uint8_t> &CmdArgs,
-                  const SmallVector<const char*>& BitcodeLibFuncs);
+                  const SmallVector<const char *> &BitcodeLibFuncs);
 
 /// Runs a regular LTO backend. The regular LTO backend can also act as the
 /// regular LTO phase of ThinLTO, which may need to access the combined index.
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 95f061036..fe1550324 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1503,7 +1503,7 @@ public:
 class InProcessThinBackend : public CGThinBackend {
 protected:
   FileCache Cache;
-  const SmallVector<const char*> &BitcodeLibFuncs;
+  const SmallVector<const char *> &BitcodeLibFuncs;
 
 public:
   InProcessThinBackend(