comgt fails to build with musl for x86_64

[zloop]

comgt.c: In function 'opengt':
comgt.c:1284:31: error: 'XCASE' undeclared (first use in this function)
   stbuf.c_lflag &= ~(ICANON | XCASE | ECHO | ECHOE | ECHONL);

XCASE is normally declared in termios.h
however the x86_64 variant is missing this for unknown reasons

with XCASE: ​http://git.musl-libc.org/cgit/musl/tree/arch/mips/bits/termios.h

without:
​http://git.musl-libc.org/cgit/musl/tree/arch/x86_64/bits/termios.h
​http://git.musl-libc.org/cgit/musl/tree/arch/i386/bits/termios.h

according to ​http://man7.org/linux/man-pages/man3/termios.3.html :
XCASE (not in POSIX; not supported under Linux);

​http://pubs.opengroup.org/onlinepubs/009695399/basedefs/termios.h.html
has XCASE removed

[nbd]

fixed in r43014