This change moves away from a classical superbuild which downloads and builds
at build time. Instead, we now follow a "Fetch Content" workflow (available as
FetchContent in CMake 3.11+) and download dependencies at config time.
Rationale: Superbuild projects have the disadvantage that projects cannot
directly access their individual declared targets. This is not a problem with
regular libraries, as those are usually/supposed to be installed. With
Sandboxed API, this is not desirable, as it has dependencies like Abseil and
glog, which are almost always consumed by including their source tree using
add_subdirectory().
Fixes#10 and makes external embedding easier.
PiperOrigin-RevId: 260129870
Change-Id: I70f295f29a6e4fc8c330512c94b01ef10c017166
* Implement add_sapi_library() similar to the Bazel rule
* Fix SuperBuild so that glog properly depends on gflags (needed for --logtostderr)
* Raise minimum required version of CMake to 3.10 (Ubuntu 18.04 LTS)
* Update sum sandbox policy to allow to get IDs and PIDs
PiperOrigin-RevId: 258124160
Change-Id: I64c2f8b27a3e842874adca9100bfce20a2b74f17
