Work around limitations of MSVC++ 6. Tickets #1429, #1437, and #1440. (CVS 2720)

FossilOrigin-Name: b2d1803c25b0b823c9cbe27989bacb730b18b45b

src/os_win.c

@@ -465,6 +465,13 @@ int sqlite3OsWrite(OsFile *id, const void *pBuf, int amt){
   return SQLITE_OK;
 }
 
+/*
+** Some microsoft compilers lack this definition.
+*/
+#ifndef INVALID_SET_FILE_POINTER
+# define INVALID_SET_FILE_POINTER ((DWORD)-1)
+#endif
+
 /*
 ** Move the read/write pointer in a file.
 */