Add Log4cpp::log4cpp imported target

cmake/Modules/FindLOG4CPP.cmake

@@ -1,4 +1,4 @@
-# Copyright (C) 2011-2018 (see AUTHORS file for a list of contributors)
+# Copyright (C) 2011-2019 (see AUTHORS file for a list of contributors)
 #
 # This file is part of GNSS-SDR.
 #
@@ -21,7 +21,10 @@
 #  LOG4CPP_INCLUDE_DIR - where to find LOG4CPP.h, etc.
 #  LOG4CPP_LIBRARIES   - List of libraries when using LOG4CPP.
 #  LOG4CPP_FOUND       - True if LOG4CPP found.
-
+#
+# Provides the following imported target:
+# Log4cpp::log4cpp
+#
 
 if(LOG4CPP_INCLUDE_DIR)
   # Already in cache, be silent
@@ -90,3 +93,18 @@ endif()
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(LOG4CPP DEFAULT_MSG LOG4CPP_INCLUDE_DIRS LOG4CPP_LIBRARIES)
+
+if (LOG4CPP_FOUND AND NOT TARGET Log4cpp::log4cpp)
+  add_library(Log4cpp::log4cpp SHARED IMPORTED)
+  set_target_properties(Log4cpp::log4cpp PROPERTIES
+      IMPORTED_LINK_INTERFACE_LANGUAGES "CXX"
+      IMPORTED_LOCATION "${LOG4CPP_LIBRARIES}"
+      INTERFACE_INCLUDE_DIRECTORIES "${LOG4CPP_INCLUDE_DIRS}"
+      INTERFACE_LINK_LIBRARIES "${LOG4CPP_LIBRARIES}"
+  )
+endif()
+
+mark_as_advanced(
+  LOG4CPP_LIBRARIES
+  LOG4CPP_INCLUDE_DIRS
+)

src/algorithms/input_filter/gnuradio_blocks/CMakeLists.txt

@@ -48,7 +48,7 @@ target_link_libraries(input_filter_gr_blocks
     PRIVATE
         Gflags::gflags
         Glog::glog
-        ${LOG4CPP_LIBRARIES}
+        Log4cpp::log4cpp
 )
 
 set_property(TARGET input_filter_gr_blocks