[NFC][clang] Fix coverity static analyzer concerns about AUTO_CAUSES_COPY
Reported by Coverity:
AUTO_CAUSES_COPY
Unnecessary object copies can affect performance.
1. [NFC] Fix auto keyword use without an & causes the copy of an object of type SimpleRegistryEntry in clang::getAttributePluginInstances()
2. [NFC] Fix auto keyword use without an & causes the copy of an object of type tuple in CheckStmtInlineAttr<clang::NoInlineAttr, 2>(clang::Sema &, clang::Stmt const *, clang::Stmt const *, clang::AttributeCommonInfo const &)
3. [NFC] Fix auto keyword use without an & causes the copy of an object of type QualType in <unnamed>::SystemZTargetCodeGenInfo::isVectorTypeBased(clang::Type const *, bool)
4. [NFC] Fix auto keyword use without an & causes the copy of an object of type Policy in <unnamed>::RISCVIntrinsicManagerImpl::InitIntrinsicList()
5. [NFC] Fix auto keyword use without an & causes the copy of an object of type pair in checkUndefinedButUsed(clang::Sema &)
Reviewed By: tahonermann
Differential Revision: <https://reviews.llvm.org/D147543>