mips64-linux-user: Fix definition of struct sigaltstack

Without this fix, qemu segfaults when emulating the sigaltstack syscall,
because it incorrectly treats the ss_flags field as 64 bits rather than 32
bits.

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>
linux-user: Fix ioctl cmd type mismatch on 64-bit targets

linux-user passes the cmd argument of the ioctl syscall as a signed long,
but compares it to an unsigned int when iterating through the ioctl_entries
list.  When the cmd is a large value like 0x80047476 (TARGET_TIOCSWINSZ on
mips64) it gets sign-extended to 0xffffffff80047476, causing the comparison
to fail and resulting in lots of spurious "Unsupported ioctl" errors.
Changing the target_cmd field in the ioctl_entries list to a signed int
causes those values to be sign-extended as well during the comparison.

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>