news: fixed weaknesses in build system and testsuite

news: fixed weaknesses in build system and testsuite

* NEWS (Bugs fixed in 1.12.1): Report that several weaknesses in the
Automake's own build system and test suite have been fixed.  See for
example recent commits:
  - commit v1.12-5-geb7e8f3, for bug#11345
  - commit v1.12-5-g63e07a9, for bug#11346
  - commit v1.12-5-gf31fe4f
  - commit v1.12-10-gab14841
  - commit v1.12-19-g807f3cf, for bug#11369
  - commit v1.12-20-gd330368, for bug#11369
  - bug#11387, pre-emptively solved by commit v1.12-4-g444618b

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>