cppcheck: silence warnings in compilerplugins

mostly missing explicit before ctors and
uninitialized member vars

one odd use of std::find
> compilerplugins/clang/implicitboolconversion.cxx
> 800 stlIfFind warning	Suspicious condition.
> The result of find() is an iterator, but it is not properly checked.

Change-Id: Iade53494cd7fe8ddb0e110e431449ae5a517fe3b
Reviewed-on: https://gerrit.libreoffice.org/24398
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/staticanonymous.cxx

@@ -21,7 +21,7 @@ class StaticAnonymous
     , public Plugin
     {
     public:
-        StaticAnonymous( const InstantiationData& data );
+        explicit StaticAnonymous( const InstantiationData& data );
         virtual void run() override;
         bool VisitFunctionDecl( FunctionDecl* func );