Lagom+CMake: Propagate dependencies for generated custom targets

We have logic for serenity_generated_sources which works well for source
files that are specified in GENERATED_SOURCES prior to calling
serenity_lib or serenity_bin. However, code generated with
invoke_generator, and the LibWeb generators do not always follow the
pattern of the IDL and GML files.

For the LibWeb generators, we can just add_dependencies to LibWeb at the
time we declare the generate_Foo custom target. However for LibLocale,
LibTimeZone, and LibUnicode, we don't have the name of the target
available, so export the name in a variable to set into
GENERATED_SOURCES.

To make this work for Lagom, we need to make sure that lagom_lib and
serenity_bin in Lagom/CMakeLists.txt call serenity_generated_sources on
the target.

This enables the Xcode generator on macOS hosts, at least for Lagom.

Userland/Libraries/LibLocale/CMakeLists.txt

@@ -2,13 +2,16 @@ include(${SerenityOS_SOURCE_DIR}/Meta/CMake/locale_data.cmake)
 
 if (DEFINED LOCALE_DATA_SOURCES)
     set(SOURCES ${LOCALE_DATA_SOURCES})
+    set(GENERATED_SOURCES ${CURRENT_LIB_GENERATED})
     if (SERENITYOS)
         serenity_lib(LibLocaleData localedata)
     else()
         add_library(LibLocaleData OBJECT ${SOURCES})
+        serenity_generated_sources(LibLocaleData)
     endif()
     target_compile_options(LibLocaleData PRIVATE -g0 -Os -Wno-parentheses-equality)
     target_link_libraries(LibLocaleData LibCore LibTimeZone)
+    unset(GENERATED_SOURCES)
 endif()
 
 set(SOURCES

Userland/Libraries/LibTimeZone/CMakeLists.txt

@@ -4,8 +4,10 @@ set(SOURCES
     TimeZone.cpp
     ${TIME_ZONE_DATA_SOURCES}
 )
+set(GENERATED_SOURCES ${CURRENT_LIB_GENERATED})
 
 add_library(LibTimeZone OBJECT ${SOURCES})
+serenity_generated_sources(LibTimeZone)
 target_compile_definitions(LibTimeZone PRIVATE ENABLE_TIME_ZONE_DATA=$<BOOL:${ENABLE_TIME_ZONE_DATABASE_DOWNLOAD}>)
 
 # NOTE: These objects are used by the DynamicLoader, which is always built without coverage instrumentation.

Userland/Libraries/LibUnicode/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SOURCES
     Normalize.cpp
     ${UNICODE_DATA_SOURCES}
 )
+set(GENERATED_SOURCES ${CURRENT_LIB_GENERATED})
 
 serenity_lib(LibUnicode unicode)
 target_link_libraries(LibUnicode LibCore)