message: depends: Add comment about cache invalidation
diff: @@ -127,6 +127,8 @@ $(host_arch)_$(host_os)_id_string+=$(shell $(host_RANLIB) --version 2>/dev/null)
  $(host_arch)_$(host_os)_id_string+=$(shell $(host_STRIP) --version 2>/dev/null)
  ifneq ($(strip $(FORCE_USE_SYSTEM_CLANG)),)
  +# Make sure that cache is invalidated when switching between system and
  +# depends-managed, pinned clang
  build_id_string+=system_clang
  $(host_arch)_$(host_os)_id_string+=system_clang
  endif
  