[libiberty] output empty args as a pair of quotes

writeargv writes out empty arguments in a way that expandargv skips
them instead of preserving them.  Fixed by writing out a pair of
quotes for them.


for  libiberty/ChangeLog

	* argv.c (writeargv): Output empty args as "".

libiberty/ChangeLog

+2020-01-23  Alexandre Oliva <oliva@adacore.com>
+
+	* argv.c (writeargv): Output empty args as "".
+
 2020-01-01  Jakub Jelinek  <jakub@redhat.com>
 
 	Update copyright years.

libiberty/argv.c

@@ -327,6 +327,14 @@ writeargv (char * const *argv, FILE *f)
           arg++;
         }
 
+      /* Write out a pair of quotes for an empty argument.  */
+      if (arg == *argv)
+	if (EOF == fputs ("\"\"", f))
+	  {
+	    status = 1;
+	    goto done;
+	  }
+
       if (EOF == fputc ('\n', f))
         {
           status = 1;