Roll-back r250822.

Summary: It breaks the build for the ASTMatchers

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D13893

llvm-svn: 250827
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 1696e36..d3d7185 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -2841,7 +2841,7 @@
 #else // NDEBUG
 
 ASTUnit::ConcurrencyState::ConcurrencyState() { Mutex = nullptr; }
-ASTUnit::ConcurrencyState::~ConcurrencyState() = default;
+ASTUnit::ConcurrencyState::~ConcurrencyState() {}
 void ASTUnit::ConcurrencyState::start() {}
 void ASTUnit::ConcurrencyState::finish() {}