compiler: avoid barfing when config.h & the current -std= mode mismatch

compiler: avoid barfing when config.h & the current -std= mode mismatch

Add a bunch of __ for all the attribute members.

Lets us keep working even if configurator is called with different
CFLAGS than the build of a file which includes compiler.h

Idealy, we (people using ccan) wouldn't let this happen, however I don't
see any reason /not/ to avoid build breakage in the above case.

Long term, it might make sense to plug some logic into configurator's
config.h (or a cc wrapper, so something else) to warn when the current
flags don't look the same as the ones used to generate config.h

CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Cody P Schafer <dev@codyps.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>