ld: implement support for exposing ld functions to loaded executables

sys/ld/CMakeLists.txt

@@ -12,8 +12,12 @@ target_link_libraries(ld
 	interface::fs)
 
 target_compile_options(ld PRIVATE
+	-fvisibility=hidden
 	-fPIC -fno-stack-protector -nostdlib -ffreestanding)
 target_link_options(ld PRIVATE
+	-fvisibility=hidden -Wl,--exclude-libs,ALL
+	# -Wl,--entry="_ld_start"
+	-T ${CMAKE_CURRENT_SOURCE_DIR}/arch/${CMAKE_SYSTEM_PROCESSOR}/layout.ld
 	-fPIC -nostdlib -ffreestanding -Wl,-shared)
 
 sysroot_add_program(