Meta: Move all options to targetname_options.cmake files

This common strategy of having a serenity_option() macro defined in
either the Lagom or top level CMakeLists.txt allows us to do two things:

First, we can more clearly see which options are Serenity-specific,
Lagom-specific, or common between the target and host builds.

Second, it enables the upcoming SuperBuild changes to set() the options
in the SuperBuild's CMake cache and forward each target's options to the
corresponding ExternalProject.

Meta/Lagom/CMakeLists.txt

@@ -8,7 +8,6 @@ project(
     LANGUAGES C CXX
 )
 
-option(ENABLE_LAGOM_CCACHE "Enable ccache for Lagom builds" OFF)
 option(BUILD_SHARED_LIBS "Build shared libraries instead of static libraries" ON)
 if (ENABLE_OSS_FUZZ)
     set(BUILD_SHARED_LIBS OFF) # Don't use shared libraries on oss-fuzz, for ease of integration with their infrastructure
@@ -26,6 +25,14 @@ get_filename_component(
 
 list(APPEND CMAKE_MODULE_PATH "${SERENITY_PROJECT_ROOT}/Meta/CMake")
 
+if(NOT COMMAND serenity_option)
+    macro(serenity_option)
+        set(${ARGV})
+    endmacro()
+endif()
+
+include(lagom_options)
+
 find_package(Threads REQUIRED)
 
 if (ENABLE_LAGOM_CCACHE)