CMake: Improve adding external libraries to wx-config

Don't add -l to libraries already containing it (for example -lpthread).
Change libraries with format libName.so or libName.a to -lName,
configure also uses -l for these libraries. Account for possible invalid
libraries (Name-NOTFOUND) which could happen with imported libraries,
for example OpenGL::OpenGL.

Closes https://github.com/wxWidgets/wxWidgets/pull/2359

build/cmake/config.cmake

@@ -42,7 +42,13 @@ macro(wx_get_dependencies var lib)
             else()
                 get_filename_component(dep_name ${dep} NAME)
             endif()
+            if(dep_name MATCHES "^-l(.*)" OR  dep_name STREQUAL "libc.so")
+                wx_string_append(${var} "${dep_name} ")
+            elseif(dep_name MATCHES "^lib(.*)(.so|.a)")
+                wx_string_append(${var} "-l${CMAKE_MATCH_1} ")
+            elseif(dep_name)
                 wx_string_append(${var} "-l${dep_name} ")
+            endif()
         endforeach()
         string(STRIP ${${var}} ${var})
     endif()