[llvm] [CodeGen] Port `ShadowStackGCLowering` to new pass manager (PR #75324)

[Matt Arsenault via llvm-commits]

================
@@ -170,7 +212,7 @@ Type *ShadowStackGCLowering::GetConcreteStackEntryType(Function &F) {
 
 /// doInitialization - If this module uses the GC intrinsics, find them now. If
 /// not, exit fast.
-bool ShadowStackGCLowering::doInitialization(Module &M) {
+bool ShadowStackGCLoweringImpl::doInitialization(Module &M) {
   bool Active = false;
   for (Function &F : M) {
     if (F.hasGC() && F.getGC() == std::string("shadow-stack")) {
----------------
arsenm wrote:

existing issue but this doesn't need the std::string?

https://github.com/llvm/llvm-project/pull/75324