Export: Report error on relative include with genex.

Diagnostics which check the sanity of exported include paths
previously skipped over any path containing a generator expression.

Introduce a policy to issue an error message in such cases.

The export files created in the OLD behavior are not usable, because
they contain relative paths or paths to the source or build location
which are not suitable for use on installation. CMake will report an
error on import.

1 files changed, 7 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMP0041/empty.cpp b/Tests/RunCMake/CMP0041/empty.cpp
new file mode 100644
index 0000000..bfbbdde
--- /dev/null
+++ b/Tests/RunCMake/CMP0041/empty.cpp
@@ -0,0 +1,7 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int empty()
+{
+  return 0;
+}