Mark empty default constructors as =default if it makes the type POD

NFC

llvm-svn: 234694
diff --git a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
index 129afe2..b94124f 100644
--- a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -163,7 +163,7 @@
     static const char *const BlockTag;
     static const char *const EdgeTag;
 
-    GCOVRecord() {}
+    GCOVRecord() = default;
 
     void writeBytes(const char *Bytes, int Size) {
       os->write(Bytes, Size);