Build only a subset of components by default

[ekilmer]

The way the Makefiles in upstream are constructed require us to rebuild the same source files for each component with slightly different compile definitions. This isn't a problem per se, but it can be time consuming if another project wants to use CMake's ExternalProject command (rather than add_subdirectory, because ExternalProject gives a lot more control over the build environment for separate settings than the main project, etc.).

Professional CMake A Practical Guide, 10th ed. gives a good summary:

The ExternalProject module’s main purpose is to enable downloading and building external projects that cannot be easily made part of the main project directly. The external project is added as its own separate child build, effectively isolated from the main project and treated more or less as a black box. This means it can be used to build projects for a different architecture, different build settings or even to build a project with a build system other than CMake. It can also be used to handle a project that defines targets or install components that clash with those of the main project.

I think the default, top-level build (cmake -B build -S .) should include all of the same targets we do now, but there should be options that have default values dependent on CMake's PROJECT_IS_TOP_LEVEL variable. All target options are ON when the project is top-level, but it should be possible to turn them off as well. The following are a list of variables that could be used for target groups (discussion is appreciated for use-cases I might not have thought about):

• sleigh_BUILD_SLA_FILES - Toggle for compiling sleigh files (implies the compiler is built)
  • Use-case: Someone doesn't want to use these sla files
• sleigh_BUILD_SLA_COMPONENTS - Toggle for all slaspec components (compiler, library, slafiles); implies sleigh_BUILD_SLA_FILES
  • Use-case: Someone wants to compile their own slaspec files and also use the library to do stuff with them (could turn off sleigh_BUILD_SLA_FILES manually if they don't want/need our sla files
• sleigh_BUILD_DECOMPILER_COMPONENTS - Toggle for building all decompiler components (decompiler, library)
• sleigh_BUILD_EXTRA_TOOLS - Toggle for building and including all other tools, like the lifter

The above variables will also affect how we handle the installation procedure. It would also make sense to use CMake's install COMPONENTS to let users know which components are installed or not for a configured distribution.

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Final note, the releases on this repo will be fully-featured. This issue is to mainly help people who want/need to build from source and prevent time-consuming target building for targets they don't need.