The Java enums are very different from the C model. As a consequence,
one cannot "build" an enum directly from an integer, we must retrieve
it. That's the purpose of the SymbolType.get class method.
* data/skeletons/java.m4 (b4_symbol_enum, b4_case_code_symbol)
(b4_declare_symbol_enum): New.
* data/skeletons/lalr1.java: Use SymbolType,
SymbolType.YYSYMBOL_YYEMPTY, etc.
* examples/java/calc/Calc.y, tests/local.at: Adjust.