Make the yacc skeleton aware of C++. It was previously broken in the

YYDEBUG case (getenv() declared wrong).

usr.bin/yacc/skeleton.c

@@ -120,13 +120,24 @@ char *body[] =
     "#define YYREJECT goto yyabort",
     "#define YYACCEPT goto yyaccept",
     "#define YYERROR goto yyerrlab",
+    "/* cfront 1.2 defines \"c_plusplus\" instead of \"__cplusplus\" */",
+    "#ifdef c_plusplus",
+    "#ifndef __cplusplus",
+    "#define __cplusplus",
+    "#endif",
+    "#endif",
+    "#ifdef __cplusplus",
+    "extern \"C\" { char *getenv(const char *); }",
+    "#else",
+    "extern char *getenv();",
+    "#endif",
+    "",
     "int",
     "yyparse()",
     "{",
     "    register int yym, yyn, yystate;",
     "#if YYDEBUG",
     "    register char *yys;",
-    "    extern char *getenv();",
     "",
     "    if (yys = getenv(\"YYDEBUG\"))",
     "    {",