This creates function 'add_external_project_step' to centralize creation
of external project steps. Users may call it to add custom steps to
external project builds.
The add_external_project function parses its arguments and puts them in
properties of the target it creates. This factors out implementation of
the behavior for use by other functions in the module.
The patch step runs parallel to the update step since it does not make
sense to have both. Configuration of the step requires specification of
a PATCH_COMMAND argument to add_external_project.
This rewrites the keyword/argument parsing and handling in the
AddExternalProject module to use arguments more literally:
- The strict keyword-value pairing is gone in favor of keywords with
arbitrary non-keyword values. This avoids requiring users to escape
spaces and quotes in command lines.
- Customized step command lines are now specified with a single
keyword <step>_COMMAND instead of putting the arguments in a
separate entry (previously called <step>_ARGS).
- Build step custom commands now use VERBATIM mode so that arguments
are correctly escaped on the command line during builds.
This teaches AddExternalProject to run "$(MAKE)" for build and install
steps of CMake-based external projects when using a Makefile generator.
It allows the external project to participate in a parallel make invoked
on the superproject.
This uses the get_property command to simplify property lookup in the
AddExternalProject module. It distinguishes for build and install
argument properties the cases of unset and set to empty.
Brad King
David Cole