LXT2 file size limit can be set by environment variable.

The LXT2 writer allows for splitting the output file into multiple
output files. The size of that output file was fixed, but needs to
be controlled by an environment variable.

vpi/sys_lxt2.c

@@ -440,10 +440,24 @@ static void *close_dumpfile(void)
 
 static void open_dumpfile(vpiHandle callh)
 {
+      off_t use_file_size_limit = lxt2_file_size_limit;
       if (dump_path == 0) dump_path = strdup("dump.lx2");
 
       dump_file = lxt2_wr_init(dump_path);
 
+      if (getenv("LXT_FILE_SIZE_LIMIT")) {
+	    const char*limit_string = getenv("LXT_FILE_SIZE_LIMIT");
+	    char*ep;
+	    use_file_size_limit = strtoul(limit_string,&ep,0);
+	    if (use_file_size_limit == 0 || ep[0] != 0) {
+		  vpi_printf("LXT2 Warning: %s:%d: LXT_FILE_SIZE_LIMIT is invalid: %s\n",
+			     vpi_get_str(vpiFile, callh),
+			     (int)vpi_get(vpiLineNo, callh),
+			     limit_string);
+		  use_file_size_limit = lxt2_file_size_limit;
+	    }
+      }
+
       if (dump_file == 0) {
 	    vpi_printf("LXT2 Error: %s:%d: ", vpi_get_str(vpiFile, callh),
 	               (int)vpi_get(vpiLineNo, callh));
@@ -462,7 +476,7 @@ static void open_dumpfile(vpiHandle callh)
 	    lxt2_wr_set_initial_value(dump_file, 'x');
 	    lxt2_wr_set_compression_depth(dump_file, 4);
 	    lxt2_wr_set_partial_on(dump_file, 1);
-	    lxt2_wr_set_break_size(dump_file, lxt2_file_size_limit);
+	    lxt2_wr_set_break_size(dump_file, use_file_size_limit);
 
             atexit((void(*)(void))close_dumpfile);
       }