Improve plugin.cmake dependency handling.

• Fix definition of _FOUND macro for lowercase dependencies.
• Support dependencies that are targets, just add them using target_add_libraries, no guessing of global variables required.

CI: https://www.graphics.rwth-aachen.de:9000/OpenFlipper-Free/OpenFlipper-Free/pipelines/12053

cmake/plugin.cmake

@@ -207,7 +207,7 @@ macro (_check_plugin_deps _prefix _optional )
 
        if ( ${_optional} STREQUAL "TRUE"  )
 
-         if ( ${_VAL}_FOUND )
+           if ( ${_VAL}_FOUND OR ${_val}_FOUND)
 
            # Optional dependency found and recursive found, so add definition to enable it
            if ( ${_optional} STREQUAL "TRUE" )
@@ -276,6 +276,9 @@ macro (_check_plugin_deps _prefix _optional )
 
         if (${_val}_FOUND OR ${_VAL}_FOUND)
           foreach (_name ${_val} ${_VAL})
+            if (TARGET ${_name})
+                list(APPEND ${_prefix}_DEPS_TARGETS ${_name})
+            endif()
             if (DEFINED ${_name}_INCLUDE_PATH)
               list (APPEND ${_prefix}_DEPS_INCDIRS "${${_name}_INCLUDE_PATH}")
             endif ()
@@ -677,6 +680,10 @@ function (_build_openflipper_plugin plugin)
       endif()
     endif()
 
+    if(${_PLUGIN}_DEPS_TARGETS)
+        target_link_libraries(Plugin-${plugin} ${${_PLUGIN}_DEPS_TARGETS})
+    endif()
+
     # append compiler and linker flags from plugin dependencies
 
     list(APPEND ${_PLUGIN}_DEPS_COMPILE_DEFINITIONS ${${_PLUGIN}_CDEFINITIONSADD} )