Minor fixups to get 'make maintainer-check' to work.

* configure.ac: Don't use -Wnested-externs, as it's incompatible
with the new verify.h implementation.
* data/c.m4 (b4_yy_symbol_print_generate): YYUSE (yyoutput).
* data/glr.c (YYUSE): Depend on __GNUC__ as well.
* data/yacc.c (YYUSE): Likewise.
* data/lalr1.cc (yysyntax_error_): YYUSE (yystate).
* lib/subpipe.c (end_of_output_subpipe): The args are unused.
* src/parse-gram.y (declaration): Don't pass a string constant
to a function that expects char *, since GCC might complain
about the constant value.
* src/reader.c (symbol_typed_p): Add parens to pacify GCC.
* tests/cxx-type.at (_AT_TEST_GLR_CXXTYPES): #undef yylloc and yylval
before #defining them.
* tests/glr-regression.at
(Incorrectly initialized location for empty right-hand side in GLR):
In yyerror, use the msg arg.
(Corrupted semantic options if user action cuts parse):
(Incorrect lookahead during deterministic GLR):
(Incorrect lookahead during nondeterministic GLR):
Don't name a local var 'index'; it shadows string.h's 'index'.

data/glr.c

@@ -253,7 +253,7 @@ b4_syncline([@oline@], [@ofile@])
 #endif
 
 /* Suppress unused-variable warnings by "using" E.  */
-#ifndef lint
+#if !defined (lint) || defined (__GNUC__)
 # define YYUSE(e) ((void) (e))
 #else
 # define YYUSE(e) /* empty */
@@ -1103,7 +1103,7 @@ yynewGLRStackItem (yyGLRStack* yystackp, yybool yyisState)
 
 /** Add a new semantic action that will execute the action for rule
  *  RULENUM on the semantic values in RHS to the list of
- *  alternative actions for STATE.  Assumes that RHS comes from 
+ *  alternative actions for STATE.  Assumes that RHS comes from
  *  stack #K of *STACKP. */
 static void
 yyaddDeferredAction (yyGLRStack* yystackp, size_t yyk, yyGLRState* yystate,
@@ -1536,7 +1536,7 @@ yysplitStack (yyGLRStack* yystackp, size_t yyk)
       yybool* yynewLookaheadNeeds;
 
       yynewStates = NULL;
-      
+
       if (yystackp->yytops.yycapacity
 	  > (YYSIZEMAX / (2 * sizeof yynewStates[0])))
 	yyMemoryExhausted (yystackp);