These are only used for type checking, so don't bother importing them at
runtime.
Generally add future annotations at the same time, to make sure that
existing uses of these imports don't need to be quoted.
This removes the warning when using default_options without fallback
kwarg completely because a subproject does not know if the main project
has an implicit fallback or not, so it could set default_options even if
not fallback is available at all.
Fixes: #9278
It should build the fallback subprject with default_library=static and
override the dependency for both static=True and static kwarg not given.
Fixes: #8050.
The dependency lookup is a lot of complex code. This refactor it all
into a single file/class outside of interpreter main class. This new
design allows adding more fallbacks candidates in the future (e.g. using
cc.find_library()) but does not yet add any extra API.
Eli Schwartz
Dylan Baker
Thomas Heijligen
Xavier Claessens
Daniel Mensinger