Also, make sure that `make dist` generates a correct tarball even if
the C++ compiler does not work.
Reported by Nelson H. F. Beebe.
* m4/cxx.m4 (BISON_CXX_WORKS): Define to true/false instead of
true/exit 77. The latter is too dangerous to use (it directly quits).
(ENABLE_CXX): New name for the Automake conditional, for consistency
with ENABLE_CXX11 etc.
* tests/local.at (AT_COMPILE, AT_COMPILE_CXX): Adjust to the new
semantics of BISON_CXX_WORKS.
* examples/c++/local.mk: Skip the variant test if C++ does not work.
* examples/calc++/local.mk: Likewise.
The CI is using Flex 2.5.35. And ICC is too picky for it. Let's stop
making these warnings errors. I wish I could disable them in the
source files using the ICC version and the Flex version, but ICC's
pragma support is unclear, and I'm tired of fighting it.
* configure.ac (FLEX_SCANNER_CXXFLAGS): Make warnings warnings.
* examples/c++/local.mk: Comment changes.
Suggested by Victor Khomenko.
http://lists.gnu.org/archive/html/bug-bison/2018-08/msg00037.html
* doc/bison.texi (A Simple C++ Example): New.
* examples/c++/local.mk, examples/c++/simple.test: New.
Extract, check, and install this new example.
* examples/local.mk: Adjust.
* examples/test: Adjust to the case where the dirname differs
from the test name.
