Remove or indent #define GNU_SOURCE

It is only needed in files designed to be usable in standalone
compilation. In those files the #ifdefinery is indented. When
compiling in-tree, GNU_SOURCE is always defined, so remove one
definition.
core/smack: downgrade info to debug

BogdanR> I think it's cool it supports SMACK and that it encourages
         them to use a propper mount point for smackfs but I don't
         think it's cool that it's printing on the screen even when
         I parse quiet to the kernel that "SMACK support is not
         enabled ...".