Make every operator bool() explicit

operator bool() is a trap, but with explicit it's far safer,
and we can use that now.

Change-Id: I4e58631c94e87c00256c3ab3cff4fd2c5f632713
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/3rdparty/cplusplus/FullySpecifiedType.h

@@ -33,7 +33,7 @@ public:
     ~FullySpecifiedType();
 
     bool isValid() const;
-    operator bool() const;
+    explicit operator bool() const;
 
     Type *type() const;
     void setType(Type *type);