frontend: line-ed: move platform-specific code to separate directory

frontend/CMakeLists.txt

@@ -1,6 +1,15 @@
-file(GLOB_RECURSE ivy_sources *.c *.h)
+string(TOLOWER ${CMAKE_SYSTEM_NAME} system_name)
 
-add_executable(ivy ${ivy_sources})
+file(GLOB ivy_sources
+	*.c *.h
+	cmd/*.c cmd/*.h
+	line-ed/*.c line-ed/*.h)
+
+file(GLOB_RECURSE sys_sources
+	sys/${system_name}/*.c
+	sys/${system_name}/*.h)
+
+add_executable(ivy ${ivy_sources} ${sys_sources})
 target_link_libraries(
 	ivy
 	ivy-rt