Add assertions to verify that we are not trying to instantiate a nontemplate in Sema::InstantiateTemplateDecl.
Add assertions to verify that we are not trying to instantiate a
nontemplate in Sema::InstantiateTemplateDecl.

This should make the issue in PR10026 more visible, although it's not
going to fix it because something is violating this precondition.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@132208 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang