Create external/Install/{lib|include}

These files are expected to exist for current cmake rules and cmake
will warn if they do not exist.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

CMakeLists.txt

@@ -286,6 +286,9 @@ set_property(DIRECTORY PROPERTY EP_BASE ${ep_base})
 # add external project install folders to build
 link_directories(${ep_base}/Install/lib)
 include_directories(${ep_base}/Install/include)
+# add the directories so cmake won't warn
+execute_process(COMMAND cmake -E make_directory ${ep_base}/Install/lib)
+execute_process(COMMAND cmake -E make_directory ${ep_base}/Install/include)
 
 #=============================================================================
 # subdirectories