llnode warnings during compilation process

[Drieger]

Current compilation process throws some warnings. Wouldn't it be a good approach to prevent merge of PRs that introduce new warnings? Or maybe add it to the test pipeline?

Current warnings are as follow:

llv8.h:395:17: warning: inline function ‘llnode::v8::String llnode::v8::ScopeInfo::ContextLocalName(int, int, int, llnode::Error&)’ used
 but never defined

llv8.h:410:16: warning: inline function ‘llnode::v8::Value llnode::v8::Context::ContextSlot(int, llnode::Error&)’ used but never defined

llv8.cc:107:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   return *reinterpret_cast<double*>(&value);

llv8.cc:1969:14: warning: variable ‘value’ set but not used [-Wunused-but-set-variable]

llscan.cc:1468:8: warning: variable ‘done’ set but not used [-Wunused-but-set-variable]

llscan.cc:528:36: warning: ‘scanner’ may be used uninitialized in this function [-Wmaybe-uninitialized]

[joyeecheung]

I'd +1 to fix them and add -Werror in our CI builds (probably not for the releases though)