Tests: Add case for IMPLICIT_DEPENDS in custom target

Use the `IMPLICIT_DEPENDS` option of `add_custom_command` and place the
command in a custom target.  Verify that `INCLUDE_DIRECTORIES` of that
custom target are honored.  This is a case that was not really designed
to work but happens to work, is useful, and makes sense.  Add a test
case make sure it continues to work.

Issue: #16830

1 files changed, 6 insertions, 0 deletions

diff --git a/Tests/RunCMake/BuildDepends/MakeCustomIncludes.cxx b/Tests/RunCMake/BuildDepends/MakeCustomIncludes.cxx
new file mode 100644
index 0000000..9a0edef
--- /dev/null
+++ b/Tests/RunCMake/BuildDepends/MakeCustomIncludes.cxx
@@ -0,0 +1,6 @@
+#include "MakeCustomIncludes.h"
+
+int main()
+{
+  return MakeCustomIncludes();
+}