- move dependency properties (libs, libdirs, C flags, header dirs,
pkg-config module names) from global lists to imported target
`INTERFACE` properties. Rework FInd modules to return their results
like this and update the libssh2 build process to use it. It makes
Find modules re-usable from the cmake-config script by libssh2
consumers, to integrate with libssh2 dependencies.
- define libssh2 dependencies as "imported targets" by the name:
`libssh2::<depname>`, e.g. `libssh2::libgcrypt`.
- cmake-config: add fall-back logic for CMake without
CMP0099 (v3.17 2020-03-20) to set lib directories.
- generate `libssh2.pc` based on imported target properties (instead of
global lists).
- add target property dump debug function.
- ci/GHA: also test cmake integration on macOS.
Follow-up to 96d7f404e7#1534Closes#1535
df0563a857