Make MetaPhyscL Available to Applications

[pbauman]

@roystgnr wrote in grinsfem/grins#410

We're also now incompatible with the newest Antioch master, thanks to my mistake - when Antioch is built with MetaPhysicL, it then depends on metaphysicl/compare_types.h, but we don't have any antioch_config function and so there's no way for us to automatically pass on the header directories for that dependency. Not sure what the best fix is.

@pbauman responded with

My knee-jerk reaction is to update the antioch.m4 in libantioch to include the relevant headers if Antioch is using MetaPhyscL. That way, the user shouldn't need to do anything (other than updating their antioch.m4 installation) since MetaPhyscL is header-only.

Further discussions can take place here.