Make calculation of link-interface-dependent properties type-sensitive.
Add the COMPATIBLE_INTERFACE_STRING property.
target_link_libraries: Document that new sigs privatize old (#13876)

Explain in the documentation for the legacy signature

 target_link_libraries(foo bar)

that the other signatures like

 target_link_libraries(foo LINK_INTERFACE_LIBRARIES ...)
 target_link_libraries(foo LINK_PRIVATE ...)

will set the LINK_INTERFACE_LIBRARIES target property and therefore make
libraries specified only by the legacy signature private.
doc: fix linebreaks in generator expression documentation
ProcessorCount test: fix path to cmsysTestsCxx executable

Use a generator expression to get the real place of this target instead of
guessing it wrong.
ProcessorCount test: require SystemInformation process to work

Currently this silently fails on some systems. Make sure those things get
noticed so we can fix that.
Merge topic 'compatible-interface-strings'

2fb2c32 Add the COMPATIBLE_INTERFACE_STRING property.
cd66b91 Make calculation of link-interface-dependent properties type-sensitive.
Merge topic 'doc-link-interface'

f032fb9 target_link_libraries: Document that new sigs privatize old (#13876)
Merge topic 'generator-expression-lf'

6c57c31 doc: fix linebreaks in generator expression documentation
Merge topic 'debug-ProcessorCount'

4d0e2e8 ProcessorCount test: require SystemInformation process to work
e03f83f ProcessorCount test: fix path to cmsysTestsCxx executable