tweak for cpp error reporting

[Zack Weinberg <zack at wolery dot cumb dot org>]

This makes error messages that come from -D or -A options on the
command line more user friendly.  Example of previous odd behavior:

$ ./cpp -Dfoo=bar -Dfoo=baz /dev/null
/dev/null:0: warning: `foo' redefined
warning: this is the location of the previous definition

This now comes out as

$ ./cpp -Dfoo=bar -Dfoo=baz /dev/null
<command line>: warning: `foo' redefined

It even gets this right:

$ echo '#define foo baz' | ./cpp -Dfoo=bar
<stdin>:1:15: warning: `foo' redefined
<command line>: warning: this is the location of the previous definition

zw

	* cpperror.c (cpp_file_line_for_message): If 'line' is zero,
	just print "<command line>".  If 'filename' is null or an
	empty string, print "<stdin>" for the filename.
	* cpplib.c (do_define): Don't print the 'location of the
	previous definition' message if we're still parsing the
	command line.
	(cpp_pedwarn_with_file_and_line): Always call
	cpp_file_line_for_message.

===================================================================
Index: cpperror.c
--- cpperror.c	2000/01/19 23:47:13	1.20
+++ cpperror.c	2000/01/30 03:24:39
@@ -84,7 +84,11 @@ cpp_file_line_for_message (pfile, filena
      const char *filename;
      int line, column;
 {
-  if (column > 0)
+  if (filename == 0 || *filename == '\0')
+    filename = "<stdin>";
+  if (line == 0)
+    fputs (_("<command line>: "), stderr);
+  else if (column > 0)
     fprintf (stderr, "%s:%d:%d: ", filename, line, column);
   else
     fprintf (stderr, "%s:%d: ", filename, line);
===================================================================
Index: cpplib.c
--- cpplib.c	2000/01/27 22:29:06	1.100
+++ cpplib.c	2000/01/30 03:24:40
@@ -685,7 +685,7 @@ do_define (pfile, keyword)
 		       mdef.symlen, mdef.symnam);
 	  else
 	    cpp_pedwarn (pfile, "`%.*s' redefined", mdef.symlen, mdef.symnam);
-	  if (hp->type == T_MACRO)
+	  if (hp->type == T_MACRO && CPP_OPTIONS (pfile)->done_initializing)
 	    cpp_pedwarn_with_file_and_line (pfile, hp->value.defn->file,
 					    hp->value.defn->line,
 			"this is the location of the previous definition");
@@ -3474,8 +3474,7 @@ cpp_pedwarn_with_file_and_line VPARAMS (
   if (!CPP_OPTIONS (pfile)->pedantic_errors
       && CPP_OPTIONS (pfile)->inhibit_warnings)
     return;
-  if (file != NULL)
-    cpp_file_line_for_message (pfile, file, line, -1);
+  cpp_file_line_for_message (pfile, file, line, -1);
   v_cpp_message (pfile, CPP_OPTIONS (pfile)->pedantic_errors, msgid, ap);
   va_end(ap);
 }