[SILOpt] Allow pre-specializations for _Trivial of known size (#70256)

* [SILOpt] Allow pre-specializations for _Trivial of known size

rdar://119224542

This allows pre-specializations to be generated and applied for trivial types of a shared size.

include/swift/SILOptimizer/Utils/SILOptFunctionBuilder.h

@@ -56,6 +56,9 @@ public:
   }
 
   SILModule &getModule() const { return *getPassManager().getModule(); }
+  irgen::IRGenModule *getIRGenModule() const {
+    return transform.getIRGenModule();
+  }
 
 private:
   SILPassManager &getPassManager() const {