Genex: Fix stack overflow in transitive property evaluation.

Commit v2.8.11~156^2~2 (Expand includes and defines transitively
in 'external' genexes., 2013-02-13) introduced a recursive loop
and a stack overflow during evaluation of a link implementation
which depends on a transitive property, such as

 add_library(empty1 ...)
 add_library(empty2 ...)
 target_link_libraries(empty1
   PRIVATE
     $<$<STREQUAL:$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>,/foo/bar>:empty2>
 )

There is no use-case for code like that currently, but it should not
cause a stack overflow.

Avoid the recursion by reporting an error early if a case like this
is found.

0 files changed, 0 insertions, 0 deletions