[clang] fix rsxs screensaver build

clang need to known that we use some gnu inline semantics
clang: fix declaration of default arg

depend on os/clang version it's a warning or an error:
error: addition of default argument on redeclaration makes
    this constructor a default constructor
warning: addition of default argument on redeclaration makes
    this constructor a default constructor

full errors: http://pastebin.com/tnJXZV8L