Generate VDBE code for the built-in COALESCE() and IFNULL() functions.  This
allows unused arguments to never be evaluated, which is a performance win when
the unused argument is a subquery.

FossilOrigin-Name: 30055b257c3c65f8123cad5ac6c62c4c6ca2c900
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 24debba..16c1d6b 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -959,6 +959,7 @@
 #define SQLITE_FUNC_NEEDCOLL 0x08 /* sqlite3GetFuncCollSeq() might be called */
 #define SQLITE_FUNC_PRIVATE  0x10 /* Allowed for internal use only */
 #define SQLITE_FUNC_COUNT    0x20 /* Built-in count(*) aggregate */
+#define SQLITE_FUNC_COALESCE 0x40 /* Built-in coalesce() or ifnull() function */
 
 /*
 ** The following three macros, FUNCTION(), LIKEFUNC() and AGGREGATE() are