Prefer signed types for indexes in skeletons

* NEWS: Mention this.
* data/skeletons/c.m4 (b4_int_type):
Prefer char if it will do, and prefer signed types to unsigned if
either will do.
* data/skeletons/glr.c (yy_reduce_print): No need to
convert rule line to unsigned long.
(yyrecoverSyntaxError): Put action into an int to
avoid GCC warning of using a char subscript.
* data/skeletons/lalr1.cc (yy_lac_check_, yysyntax_error_):
Prefer ptrdiff_t to size_t.
* data/skeletons/yacc.c (b4_int_type):
Prefer signed types to unsigned if either will do.
* data/skeletons/yacc.c (b4_declare_parser_state_variables):
(YYSTACK_RELOCATE, YYCOPY, yy_lac_stack_realloc, yy_lac)
(yytnamerr, yysyntax_error, yyparse): Prefer ptrdiff_t to size_t.
(YYPTRDIFF_T, YYPTRDIFF_MAXIMUM): New macros.
(YYSIZE_T): Fix "! defined YYSIZE_T" typo.
(YYSIZE_MAXIMUM): Take the minimum of PTRDIFF_MAX and SIZE_MAX.
(YYSIZEOF): New macro.
(YYSTACK_GAP_MAXIMUM, YYSTACK_BYTES, YYSTACK_RELOCATE)
(yy_lac_stack_realloc, yyparse): Use it.
(YYCOPY, yy_lac_stack_realloc): Cast to YYSIZE_T to pacify GCC.
(yy_reduce_print): Use int instead of unsigned long when int
will do.
(yy_lac_stack_realloc): Prefer long to unsigned long when
either will do.
* tests/regression.at: Adjust to these changes.

NEWS

@@ -40,6 +40,12 @@ GNU Bison NEWS
   The Java backend no longer emits code and data for parser tracing if the
   %define variable parse.trace is not defined.
 
+*** Templates prefer signed integer types
+
+  Bison templates now prefer signed to unsigned integer types when
+  either will do, as the signed types are less error-prone and allow
+  for better checking with 'gcc -fsanitize=undefined'.
+
 * Noteworthy changes in release 3.4.2 (2019-09-12) [stable]
 
 ** Bug fixes