Description of problem:
Code generated with "bison -y" fails with g++
 
The problem originates from the fragment: /usr/share/bison/yacc.c:1116
 
    #if defined (__GNUC_MINOR__) && 2093 <= (__GNUC__ * 1000 + __GNUC_MINOR__)
      __attribute__ ((__unused__))
    #endif
 
The "__attribute__ ((__unused__))" feature is supported by gcc, but 
apparently not by g++.

Version-Release number of selected component (if applicable):
bison-1.875-2
gcc-3.2.3-4

How reproducible:
100%

Steps to Reproduce:
1.   --- test.c ---

    int main() {
    yyerrlab1:
    __attribute__ ((__unused__))
        goto yyerrlab2;
    yyerrlab2:
        return(0);
    }

2.  gcc -Wall test.c
3.  g++ -Wall test.c
    
Actual results:
gcc OK
g++ fails with:

    test.c: In function `int main()':
    test.c:4: syntax error before `goto'
    test.c:5: warning: label `yyerrlab2' defined but not used
    test.c:2: warning: label `yyerrlab1' defined but not used

Expected results:
Either g++ should support __attribute__ in the same way as gcc, or yacc.c
should take account of the different behavior.

Additional info:
g++296 fails in the same way.
Problem does not occur with bison-1.35-4, from RH8.0, which had bison.simple
instead of yacc.c.