Make iot sdk target actually use CRT library target (#321)

* Make iot sdk target actually use CRT and IoT library targets

* Do not add aws-c-iot to the root package, it is linked by leaf targets

Author: Justin Boswell

CMakeLists.txt

@@ -58,6 +58,8 @@ else()
     set(IN_SOURCE_BUILD OFF)
 endif()
 
+aws_use_package(aws-crt-cpp)
+
 add_subdirectory(jobs)
 add_subdirectory(shadow)
 add_subdirectory(discovery)