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.

1 files changed, 8 insertions, 0 deletions

diff --git a/Tests/RunCMake/TargetPropertyGeneratorExpressions/LinkImplementationCycle6-stderr.txt b/Tests/RunCMake/TargetPropertyGeneratorExpressions/LinkImplementationCycle6-stderr.txt
new file mode 100644
index 0000000..5cfeb0a
--- /dev/null
+++ b/Tests/RunCMake/TargetPropertyGeneratorExpressions/LinkImplementationCycle6-stderr.txt
@@ -0,0 +1,8 @@
+CMake Error:
+  Error evaluating generator expression:
+
+    \$<TARGET_PROPERTY:INTERFACE_INCLUDE_DIRECTORIES>
+
+  \$<TARGET_PROPERTY:...> expression in link libraries evaluation depends on
+  target property which is transitive over the link libraries, creating a
+  recursion.