headers: Add new constants in sqlext.h Required for pyodbc https://github.com/mkleehammer/pyodbc Fixes https://github.com/mingw-w64/mingw-w64/issues/93 Signed-off-by: Biswapriyo Nath <nathbappai@gmail.com> Signed-off-by: LIU Hao <lh_mouse@126.com>