[AST] Make InitListExpr::isExplicit const (NFC)
[AST] Make InitListExpr::isExplicit const (NFC)

Patch by Alexander Shaposhnikov!

Differential Revision: https://reviews.llvm.org/D23828

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@279613 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit a298b6919862309f130f496e5f36e2e0c22f72d5)

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