Add commonly required POSIX/BSD interfaces that portable command-line
utilities expect but that were missing from the C library:
- include/paths.h: _PATH_DEFPATH and the other standard default paths.
- include/sys/ttydefaults.h: BSD default control-character and terminal
flag definitions.
- include/termios.h: define the IUTF8 input flag.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
