Give internal classes hidden visibility.

Worth 100k on a linux/x86_64 Release+Asserts clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190534 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/LeaksContext.h

@@ -28,7 +28,7 @@ struct PrinterTrait<Value> {
 };
 
 template <typename T>
-struct LeakDetectorImpl {
+struct LLVM_LIBRARY_VISIBILITY LeakDetectorImpl {
   explicit LeakDetectorImpl(const char* const name = "") : 
     Cache(0), Name(name) { }