build: auto-generate perl subroutines prototypes for automake and aclocal This will allow us to avoid either using the '&foo' invocation form when invoking a subroutine before its definition, or having to maintain the list of prototypes by hand (with the risk of having it become incomplete or fall out-of-sync when future edits to the automake and aclocal scripts are done). * Makefile.am (automake, aclocal): Automatically generate a list of prototypes by looking at the subroutines definitions. * bootstrap.sh: Likewise, when generating the temporary automake and aclocal scripts used for bootstrapping. * automake.in: Add a placeholder that will be tracked by the new recipes and substituted with the computed prototypes. Remove existing prototypes, that are now superfluous. Some adjustments required by the new, more comprehensive prototypes declarations. * aclocal.in: Likewise. * maintainer/syntax-checks.mk (sc_diff_automake, sc_diff_aclocal): Adjust. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>