Have the GLR tests be `warning' checked, and fix the warnings.

Have the GLR tests be `warning' checked, and fix the warnings.
* data/glr.c (YYFPRINTF): Always define it, not only when YYDEBUG
(yyuserAction, yyreportAmbiguity): `Use' all the arguments.
(yyremoveDeletes): `yyi' and `yyj' are size_t.
Use YYFPRINTF when under if (YYDEBUG) to avoid empty `if' bodies.
(yyaddDeferredAction): static.
(yyglrReduce): yyi, yyk, amd yyposn are size_t.
(yyreportParseError): yyprefix is const.
yytokenp is used only when verbose.
(yy__GNUC__): Replace with __GNUC__.
(yypdumpstack): yyi is size_t.
(yypreference): Un-yy local variables and arguments, to avoid
clashes with `yyr1'.  Anyway, we are not in the user name space.
(yytname_size): be an int, as is compared with ints.
* tests/testsuite.at (AT_COMPILE, AT_PARSER_CHECK): New.
Use them.
* tests/cxx-gram.at: Use quotation to protect $1.
Use AT_COMPILE to enable warnings hunts.
Prototype yylex and yyerror.
`Use' argc.
Include `string.h', not `strings.h'.
Produce and prototype stmtMerge only when used.
yylex takes a location.