Move forgotten file to core library

Turns out, there was a cpp file for hte core library, so turn the
library into a static library.

common/CMakeLists.txt

@@ -388,7 +388,6 @@ set( COMMON_SRCS
     validators.cpp
     wildcards_and_files_ext.cpp
     drawing_sheet/ds_painter.cpp
-    wx_stl_compat.cpp
     wx_filename.cpp
     xnode.cpp
     )

libs/core/CMakeLists.txt

@@ -5,14 +5,14 @@ if( COMPILER_SUPPORTS_WARNINGS )
 endif()
 
 
-add_library( core INTERFACE
+add_library( core STATIC
-    # Just a header library right now
+    wx_stl_compat.cpp
 )
 
-target_link_libraries( core INTERFACE
+target_link_libraries( core PUBLIC
     ${wxWidgets_LIBRARIES}
 )
 
-target_include_directories( core INTERFACE
+target_include_directories( core PUBLIC
     ${CMAKE_CURRENT_SOURCE_DIR}/include
 )