telepathy-qt: cmake: fix CMP0046 warnings in case doxygen is not found

[Alexandr Akulich]

Module: telepathy-qt
Branch: master
Commit: 10c9bc25da7c6d86300cc492796042a438720683
URL:    http://cgit.freedesktop.org/telepathy/telepathy-qt/commit/?id=10c9bc25da7c6d86300cc492796042a438720683

Author: George Kiagiadakis <gkiagia at tolabaki.gr>
Date:   Tue Jun 21 15:10:13 2016 +0300

cmake: fix CMP0046 warnings in case doxygen is not found

---

 cmake/modules/Doxygen.cmake | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/cmake/modules/Doxygen.cmake b/cmake/modules/Doxygen.cmake
index 11962f1..bc81223 100644
--- a/cmake/modules/Doxygen.cmake
+++ b/cmake/modules/Doxygen.cmake
@@ -34,4 +34,9 @@ point to its location to enable crosslinking.")
     set(GENERATE_QHP     ${QHELPGENERATOR_FOUND})
     configure_file(doxygen.cfg.in ${CMAKE_BINARY_DIR}/doxygen.cfg)
     add_custom_target(doxygen-doc ${DOXYGEN_EXECUTABLE} ${CMAKE_BINARY_DIR}/doxygen.cfg)
+else()
+    # Suppress cmake policy CMP0046 warnings.
+    # This target is being used as a dependency in other targets,
+    # so it always needs to be available, even if empty.
+    add_custom_target(doxygen-doc)
 endif()