[sql] Import reference version of SQLite 3.7.6.3.

third_party/sqlite/sqlite-src-3070603/src/walker.c

 /*
 ** 2008 August 16
 **
 ** The author disclaims copyright to this source code.  In place of
 ** a legal notice, here is a blessing:
 **
 **    May you do good and not evil.
 **    May you find forgiveness for yourself and forgive others.
 **    May you share freely, never taking more than you give.
 **
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   rc = WRC_Continue;
   while( p  ){
     rc = pWalker->xSelectCallback(pWalker, p);
     if( rc ) break;
     if( sqlite3WalkSelectExpr(pWalker, p) ) return WRC_Abort;
     if( sqlite3WalkSelectFrom(pWalker, p) ) return WRC_Abort;
     p = p->pPrior;
   }
   return rc & WRC_Abort;
 }