Make it possible to disable the subquery-by-coroutine optimization using
sqlite3_test_control().  Remove an always-false conditional.

FossilOrigin-Name: 564631f3e45f8f8a8db69f1e0df0d1dadbad8a2c
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 20b2e71..e44ce7b 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -827,7 +827,7 @@
   unsigned int openFlags;       /* Flags passed to sqlite3_vfs.xOpen() */
   int errCode;                  /* Most recent error code (SQLITE_*) */
   int errMask;                  /* & result codes with this before returning */
-  u8 dbOptFlags;                /* Flags to enable/disable optimizations */
+  u16 dbOptFlags;               /* Flags to enable/disable optimizations */
   u8 autoCommit;                /* The auto-commit flag. */
   u8 temp_store;                /* 1: file 2: memory 0: default */
   u8 mallocFailed;              /* True if we have seen a malloc failure */
@@ -972,7 +972,8 @@
 #define SQLITE_DistinctOpt    0x0020   /* DISTINCT using indexes */
 #define SQLITE_CoverIdxScan   0x0040   /* Covering index scans */
 #define SQLITE_OrderByIdxJoin 0x0080   /* ORDER BY of joins via index */
-#define SQLITE_AllOpts        0x00ff   /* All optimizations */
+#define SQLITE_SubqCoroutine  0x0100   /* Evaluate subqueries as coroutines */
+#define SQLITE_AllOpts        0xffff   /* All optimizations */
 
 /*
 ** Macros for testing whether or not optimizations are enabled or disabled.