Add -Wextra-semi and -Wdouble-promotion
Add -Wextra-semi and -Wdouble-promotion

These flags seem to only have an effect if they're set in WARNING_CFLAGS
instead of OTHER_C_FLAGS for some reason, but WARNING_CFLAGS is a good
place to put them anyhow.

CocoaLumberjack/CocoaLumberjack,CocoaLumberjack/CocoaLumberjack,CocoaLumberjack/CocoaLumberjack,CocoaLumberjack/CocoaLumberjack