incremental compilation: save the configuration

compiler/incremental.nim

@@ -33,6 +33,7 @@ when nimIncremental:
       db*: DbConn
       w*: Writer
       r*: Reader
+      configChanged*: bool
 
   proc init*(incr: var IncrementalCtx) =
     incr.w.sstack = @[]
@@ -92,6 +93,12 @@ when nimIncremental:
       );
     """)
 
+    db.exec(sql"""
+      create table if not exists config(
+        config varchar(8000) not null
+      );
+    """)
+
     db.exec(sql"""
       create table if not exists filenames(
         id integer primary key,