dist: correct sense of no-dist-built-sources option.

dist: correct sense of no-dist-built-sources option.

Primarily from https://bugs.gnu.org/69908.

* bin/automake.in (preprocess_file) <DIST_BUILT_SOURCES>:
make the option name be "no-dist-built-sources",
per Options.pm and automake.texi; then set it with a single !.
* lib/am/distdir.am (distdir) [DIST_BUILT_SOURCES]: insert the
dependency on $(BUILT_SOURCES) when DIST_BUILT_SOURCES is true,
not false; i.e., sense was reversed.
* t/dist-no-built-sources.sh: edit the test configure.ac
in the no-dist-built-sources case. Rename the testopt value to
match the Automake option.
* NEWS: mention this.