lalr1.cc: support compilation with disabled support for exceptions

Reported by Brooks Moses <bmoses@google.com>
http://lists.gnu.org/archive/html/bison-patches/2018-02/msg00000.html

* data/lalr1.cc (YY_EXCEPTIONS): New.
Use it to disable try/catch clauses.

* doc/bison.texi (C++ Parser Interface): Document it.

* configure.ac (CXXFLAGS_NO_EXCEPTIONS): New.
* tests/atlocal.in: Receive it.
* tests/local.at (AT_FULL_COMPILE, AT_LANG_COMPILE):
Accept a new argument, extra compiler flags.
* tests/calc.at: Run the C++ calculator with exception support disabled.

configure.ac

@@ -153,6 +153,7 @@ if test "$enable_gcc_warnings" = yes; then
   # ... possiby in std=c++11 mode.
   gl_WARN_ADD([-Wno-zero-as-null-pointer-constant], [FLEX_SCANNER_CXXFLAGS])
   CXXFLAGS=$save_CXXFLAGS
+  gl_WARN_ADD([-fno-exceptions], [CXXFLAGS_NO_EXCEPTIONS])
   AC_LANG_POP([C++])
 fi