core: Make variable shadowing a compile-time error

Now that we have most of core free of shadowing, we can enable the
warning as an error to catch anything that may be remaining and also
eliminate this class of logic bug entirely.

src/core/file_sys/submission_package.h

@@ -27,7 +27,7 @@ enum class ContentRecordType : u8;
 
 class NSP : public ReadOnlyVfsDirectory {
 public:
-    explicit NSP(VirtualFile file, std::size_t program_index = 0);
+    explicit NSP(VirtualFile file_, std::size_t program_index_ = 0);
     ~NSP() override;
 
     Loader::ResultStatus GetStatus() const;