Initialize LIBOMP_INCLUDE_DIR to be used in higher scopes

Author: jprotze

runtime/src/CMakeLists.txt

@@ -161,6 +161,7 @@ if(NOT LIBOMP_LIBRARY_DIR)
 else()
   set(LIBOMP_LIBRARY_DIR ${LIBOMP_LIBRARY_DIR} PARENT_SCOPE)
 endif()
+set(LIBOMP_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
 
 # Add symbolic links to libomp
 if(NOT WIN32)