Added in version 3.25.
Specifies that a target is a system target. This has the following effects:
Entries of INTERFACE_INCLUDE_DIRECTORIES are treated as
system include directories when compiling consumers.
Entries of INTERFACE_SYSTEM_INCLUDE_DIRECTORIES are not
affected, and will always be treated as system include directories.
On Apple platforms, If the FRAMEWORK target property is true,
the frameworks directory is treated as system.
For imported targets, this property defaults to true, which means
that their INTERFACE_INCLUDE_DIRECTORIES and, if the
FRAMEWORK target property is true, frameworks directory are
treated as system directories by default. If their SYSTEM property is
false, then their INTERFACE_INCLUDE_DIRECTORIES as well as
frameworks will not be treated as system. Use the EXPORT_NO_SYSTEM
property to change how a target's SYSTEM property is set when it is
installed.
For non-imported targets, this target property is initialized from
the SYSTEM directory property when the target is created.