style: use %code for local function declarations in our parser

style: use %code for local function declarations in our parser

* src/parse-gram.y (version_check, gram_error, char_name, lloc_default):
Move their prototypes from %{...%} to %code.
(YYLLOC_DEFAULT, YY_LOCATION_PRINT): Move from %{...%} to %code.
(current_lhs): Move its implementation to the epilogue.