android: prepare simplified utf support

Add some missing mb funcs

Change-Id: Ib80ee94d0dad6bf91df780c43fdce6694a4e3d19

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>
add some mbtowc/wctomb tests

Change-Id: Id18ef71de355b8d316feafa6383f9bacd828a7fa
fix some type warnings

Change-Id: Ifb153429f8129e4da35d7e3c3186e674e7330f8d