CMake: Added gtl::gtl alias for gtl interface library (#42)

* added cmake alias for gtl library

* properly use dynamic project name for alias target

Author: M2-TE

CMakeLists.txt

@@ -74,6 +74,7 @@ set(GTL_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/include/${GTL_DIR}/phmap.hpp
 include(helpers)
 
 add_library(${PROJECT_NAME} INTERFACE)
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 target_sources(${PROJECT_NAME} INTERFACE ${GTL_HEADERS})