Cleaning up lib-src

FileDialog goes into audacity/src/widgets and the mod-* directories go into
audacity/modules.

This leaves nothing in lib-src that isn't a 3rd-party libs or supporting
files.

modules/mod-null/CMakeLists.txt

@@ -0,0 +1,58 @@
+
+set( TARGET mod-null )
+set( TARGET_ROOT ${CMAKE_CURRENT_SOURCE_DIR} )
+
+message( STATUS "========== Configuring ${TARGET} ==========" )
+
+def_vars()
+
+add_library( ${TARGET} MODULE EXCLUDE_FROM_ALL )
+
+list( APPEND SOURCES
+   PRIVATE
+      ${TARGET_ROOT}/ModNullCallback.cpp
+      ${TARGET_ROOT}/ModNullCallback.h
+)
+
+get_target_property( INCLUDES wxWidgets INTERFACE_INCLUDE_DIRECTORIES )
+list( APPEND INCLUDES
+   PUBLIC
+      ${TARGET_ROOT}
+)
+
+get_target_property( DEFINES wxWidgets INTERFACE_COMPILE_DEFINITIONS )
+list( APPEND DEFINES
+   PRIVATE
+      # This is needed until the transition to cmake is complete and
+      # the Windows pragmas are removed from ModNullCallback.cpp.
+      # Without it, the wxWidgets "debug.h" will define __WXDEBUG__
+      # which then causes this module to emit library pragmas for the
+      # debug versions of wxWidgets...even if the build is for Release.
+      wxDEBUG_LEVEL=0
+)
+
+list( APPEND LOPTS
+   PRIVATE
+      $<$<PLATFORM_ID:Darwin>:-undefined dynamic_lookup>
+)
+
+list( APPEND LIBRARIES
+   PRIVATE
+      Audacity
+      $<$<PLATFORM_ID:Windows>:wxWidgets>
+)
+
+set_target_property_all( ${TARGET} LIBRARY_OUTPUT_DIRECTORY "${_DEST}/modules" )
+set_target_properties( ${TARGET}
+   PROPERTIES
+      PREFIX ""
+      FOLDER "lib-src"
+)
+
+organize_source( "${TARGET_ROOT}" "" "${SOURCES}" )
+target_sources( ${TARGET} PRIVATE ${SOURCES} )
+target_compile_definitions( ${TARGET} PRIVATE ${DEFINES} )
+target_include_directories( ${TARGET} PRIVATE ${INCLUDES} )
+target_link_options( ${TARGET} PRIVATE ${LOPTS} )
+target_link_libraries( ${TARGET} PRIVATE ${LIBRARIES} )
+