Suppress some compiler warnings, fix few possible bugs. (#6224)

* Supress warnings on unused functions an variables

Compilation of OrcaSlicer produces 3056 warnings.
Nearly half of them related to unused functions and variables.

It is unlikely we going to clean them up since we may want to
keep code base as close to the BBS as possible

* initialize class member with correct value

* Fix memset arguments order

* Merge multiple statemensts into single

* fix -Wpessimizing-move

src/libslic3r/Extruder.cpp

@@ -9,7 +9,7 @@ double Extruder::m_share_retracted = 0.;
 Extruder::Extruder(unsigned int id, GCodeConfig *config, bool share_extruder) :
     m_id(id),
     m_config(config),
-    m_share_extruder(m_share_extruder)
+    m_share_extruder(share_extruder)
 {
     reset();