Fix build for gcc.

Fix build for gcc.

Gcc doesn't like the brace object initialization, so make all of
the Feature objects explicit.

Also, no arguments to the error_log macros make gcc unhappy, so add
an option to turn these into warnings. These will be fixed when we
add the explicit _error and _warn log functions.

Change-Id: I35af834dabb5548923e893dd980a751fdebfa13a