Silence compiler warnings

[ydah]

Before

❯ bundle exec rspec                    
....................................................../var/folders/91/c1qqv7c94yz_cp1dz10bmwq00000gp/T/test.c:1179:9: warning: variable 'yynerrs' set but not used [-Wunused-but-set-variable]
    int yynerrs = 0;
        ^
1 warning generated.
....../var/folders/91/c1qqv7c94yz_cp1dz10bmwq00000gp/T/test.c:1208:9: warning: variable 'yynerrs' set but not used [-Wunused-but-set-variable]
    int yynerrs = 0;
        ^
1 warning generated.
./var/folders/91/c1qqv7c94yz_cp1dz10bmwq00000gp/T/test.c:1196:9: warning: variable 'yynerrs' set but not used [-Wunused-but-set-variable]
    int yynerrs = 0;
        ^
1 warning generated.
..........................................................................

Finished in 6.89 seconds (files took 0.51071 seconds to load)
135 examples, 0 failures

After

❯ bundle exec rspec
.......................................................................................................................................

Finished in 5.9 seconds (files took 0.39775 seconds to load)
135 examples, 0 failures

Coverage report generated for RSpec to /Users/yudai.takada/ydah/lrama/coverage. 2482 / 2608 LOC (95.17%) covered.

[yui-knk]

Thanks!