remove ancient lint directives

* data/c++.m4, data/yacc.c: Remove surprising remains of lint
directives.

data/c++.m4

@@ -604,7 +604,7 @@ m4_define([b4_yylloc_default_define],
         {                                                               \
           (Current).begin = (Current).end = YYRHSLOC (Rhs, 0).end;      \
         }                                                               \
-    while (/*CONSTCOND*/ false)
+    while (false)
 # endif
 ]])
 

data/yacc.c

@@ -1780,8 +1780,8 @@ yyerrorlab:
   /* Pacify compilers like GCC when the user code never invokes
      YYERROR and the label yyerrorlab therefore never appears in user
      code.  */
-  if (/*CONSTCOND*/ 0)
-     goto yyerrorlab;
+  if (0)
+    goto yyerrorlab;
 
   /* Do not reclaim the symbols of the rule whose action triggered
      this YYERROR.  */