* sysdeps/unix/sysv/linux/mips/sigcontextinfo.h: Port to n32/n64.
* sysdeps/unix/sysv/linux/mips/bits/sigcontext.h: New.
* sysdeps/unix/sysv/linux/mips/sys/ucontext.h: Port to n32/n64.
(mcontext_t): Make it match the 32-bit mips kernel in o32.
* sysdeps/unix/sysv/linux/mips/sys/user.h: Bring in constants from
the mips and mips64 headers.
(struct user): Port to n32/n64.
* sysdeps/unix/sysv/linux/mips/sigcontextinfo.h: New file.
* sysdeps/unix/sysv/linux/mips/register-dump.h: New file.
* sysdeps/mips/stackinfo.h: New file.