Fix minor testsuite issues, update docs, for Yacc/Lex changes.

Fix minor testsuite issues, update docs, for Yacc/Lex changes.

* doc/automake.texi (Yacc and Lex): Mention AM_YFLAGS, YFLAGS
and AM_LFLAGS, LFLAGS in the order in which they now appear in
the rules.
* NEWS: Update.
* tests/lflags.test, tests/lflags2.test, tests/yflags.test,
tests/yflags2.test: Prefer `make -e' over `make VAR=VAL', to
please maintainer-check.  Ensure generated C files contain a
declaration, to please compilers.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>