I tried again right now and that warning doesn't come up anymore.
make all-am
make[3]: ingresso nella directory "/home/catonano/projects/guile-reader/src"
CC reader.lo
CC token-readers.lo
CC reader-lib.lo
CC compat.lo
compat.c: In function ‘tag_to_type’:
compat.c:239:2: warning: implicit declaration of function ‘scm_c_issue_deprecation_warning_fmt’; did you mean ‘scm_set_current_warning_port’? [-Wimplicit-function-declaration]
scm_c_issue_deprecation_warning_fmt
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scm_set_current_warning_port
CCLD
libguile-reader.la