Add +vhdl-work+ control to the config file.

Presumably, the user will want the ability to explicitly set the
working library location, so create a +vhdl-work+ plusarg setting
for exactly that purpose.

ivlpp/main.c

@@ -59,6 +59,8 @@ char *dep_path = NULL;
 char dep_mode = 'a';
 /* Path to vhdlpp */
 char *vhdlpp_path = 0;
+/* vhdlpp work directory */
+char *vhdlpp_work = 0;
 
 /*
  * Keep in source_list an array of pointers to file names. The array
@@ -174,6 +176,13 @@ static int flist_read_flags(const char*path)
 			vhdlpp_path = strdup(arg);
 		  }
 
+	    } else if (strcmp(cp,"vhdlpp-work") == 0) {
+		  if (vhdlpp_work) {
+			fprintf(stderr, "Ignore duplicate vhdlpp-work flags\n");
+		  } else {
+			vhdlpp_work = strdup(arg);
+		  }
+
 	    } else {
 		  fprintf(stderr, "%s: Invalid keyword %s\n", path, cp);
 	    }
@@ -403,6 +412,10 @@ int main(int argc, char*argv[])
 	    return 1;
       }
 
+      if (vhdlpp_work == 0) {
+	    vhdlpp_work = strdup("ivl_vhdl_work");
+      }
+
 	/* Pass to the lexical analyzer the list of input file, and
 	   start scanning. */
       reset_lexor(out, source_list);