main/musl: backport fixes from 1.2.0

wcwidth wrongly returned 0 for most of planes 4 and up
missing case mapping between U+03F3 and U+037F
wrong cacosh results for arguments with negative imaginary part
wrong catanf/catanl results for various classes of arguments
wrong return value for ungetc with argument outside [0,UCHAR_MAX]
posix_openpt with no ptys available produced wrong errno