Separate language option handling into 2 phases

Separate language option handling into 2 phases
We now first collect the option instructions (from the commandline,
from pragmas in source files, etc), and then later flatten them into
the list of enabled options. This will enable us to use different
standards (H98, H2010, etc) as a base upon which to apply the
instructions, when we don't know what the base will be when we start
collecting instructions.