non-recursive-gnulib-prefix-hack is deprecated

[Bruno Haible]

Hi,

hello/bootstrap.conf still uses the Gnulib module
'non-recursive-gnulib-prefix-hack'. This module is now deprecated [1].
The replacement is a gnulib-tool option '--automake-subdir'. The way
to migrate to this replacement is shown, for example, in the way GNU sed
was migrated. [2]

Bruno

[1] https://lists.gnu.org/archive/html/bug-gnulib/2021-12/msg00116.html
[2] 
https://git.savannah.gnu.org/gitweb/?p=sed.git;a=commitdiff;h=a465ca5f228eaf892f864aa46766c990bf984a99#patch1