ClangTools: Support loading exported diagnostics

Add a new toolbar button to load diagnostics exported with

   $ clang-tidy -export-fixes=/path/to/file
   $ clazy-standalone -export-fixes=/path/to/file (master version)

Change-Id: I8316fe0706a18222e68220ef4fbfdc7ae8d09804
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangtools/clangtoolsdiagnostic.h

@@ -62,6 +62,8 @@ public:
     bool hasFixits = false;
 };
 
+bool operator==(const Diagnostic &lhs, const Diagnostic &rhs);
+
 using Diagnostics = QList<Diagnostic>;
 
 quint32 qHash(const Diagnostic &diagnostic);