[libclang] Fix the mismatched delete operator for ExprEvalResult
[libclang] Fix the mismatched delete operator for ExprEvalResult

The '.stringVal' field in ExprEvalResult is allocated using new[],
but was freed using a regular delete. That caused memory leaks in
the test from r350666.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@350680 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit c3ada736c34d204768d2b6a303a191401713a958)

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang