Ensure M4 compiles correctly with -DDEBUG, and use a single
consistent definition of various /DEBUG_[A-Z]+/ symbols:
* m4/input.c: Have commented out out DEBUG_INPUT only by default.
(m4_print_token): Use m4_get_symbol_value_text and
m4_get_symbol_value_func calls instead of obsolescent VALUE_TEXT
and VALUE_FUNC respectively.
(m4__next_token): Use m4_print_token call instead of obsolescent
print_token symbol.
* m4/module.c: Have commented out out DEBUG_MODULE only by default.
* m4/output.c: Similarly for DEBUG_OUTPUT.
* m4/path.c: Similarly for DEBUG_INCL.
* m4/symtax.c: Similarly for DEBUG_SYM.
* m4/syntax.c: Similarly for DEBUG_SYNTAX.
* src/stackovf.c: Similarly for DEBUG_STACKOVF.
* m4/m4private.h (DEBUG): Add DEBUG_OUTPUT and DEBUG_STACKOVF to
preprocessor macros defined with -DDEBUG compiles.