mips: missing syscall returns wrong errno

mips: missing syscall returns wrong errno

Return -TARGET_ENOSYS instead of -ENOSYS from linux-user/main.c
   * Caused strange 'Level 2 synchronization messages' instead of
correctly reporting the syscall was missing.
   * Made glibc simply fail instead of using older syscalls

Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Wesley W. Terpstra <terpstra@debian.org>