"level" can have value "DEBUG". In some environment "DEBUG" is
used as preprocessor name to enable some debugging code.
Using -DDEBUG option (or similar) cause "DEBUG" to be defined as "1"
so "G_PASTE(G_LOG_LEVEL_, level)" will be expanded to "G_LOG_LEVEL_1"
instead of "G_LOG_LEVEL_DEBUG".
Just concatenate the two literal to avoid "DEBUG" expansion.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Victor Toso <victortoso@redhat.com>