Update reference docs to reflect code default

[sebrowne]

When investigating some behavior in Trilinos, I used the documentation to ascertain the default value of ${PROJECT_NAME}_DISABLE_ENABLED_FORWARD_DEP_PACKAGES, and determined it to be inconsistent with the "real" setting. Fix that here.

[bartlettroscoe]

@sebrowne, it appears you are correct:

TriBITS/tribits/core/package_arch/TribitsGlobalMacros.cmake

Line 218 in 06c8e1b

set(${PROJECT_NAME}_DISABLE_ENABLED_FORWARD_DEP_PACKAGES_DEFAULT OFF)

It seems the default got changed in the commit ec1d0a2 (allowing an override) but the documentation did not get updated correctly somehow and may have even been added incorrectly in commit d2214df.

[bartlettroscoe]

I updated the text to make the context for the configure error more clear.

[bartlettroscoe]

@sebrowne, what was the scenario where you hit this situation?

IMHO, automated testing processes should have this set to ${PROJECT_NAME}_DISABLE_ENABLED_FORWARD_DEP_PACKAGES=ON as it makes them much more robust. (That was our experience with CASL VERA.)

[sebrowne]

Here's the linked PR where I repair what is wrong in Trilinos:

trilinos/Trilinos#13991

It was exactly as you said, but we were sometimes setting it and sometimes not. Whether it should be set or unset long-term is a matter for future discussion, but we intend to be setting it on all CI configurations at the moment.

[bartlettroscoe]

@sebrowne, I don't see where ${PROJECT_NAME}_DISABLE_ENABLED_FORWARD_DEP_PACKAGES=ON is being set in:

https://github.com/trilinos/Trilinos/pull/13991/files

?