This fixes some CMake-3.12+-isms, like `list(JOIN ...)` and setting link
properties on OBJECT libraries.
PiperOrigin-RevId: 265033725
Change-Id: I0ee1ec0e1b1097ea8226ad6fdeff794a97c2881b
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
