Fix crash in clang.
Fix crash in clang.

This happened during a recent refactor.  toStringRefArray() returns
a vector<StringRef>, which was being implicitly converted to an
ArrayRef<StringRef>, and then the vector was immediately being
destroyed, so the ArrayRef<> was losing its backing storage.
Fix this by making sure the vector gets permanent storage.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@336219 91177308-0d34-0410-b5e6-96231b3b80d8

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