linux-user: rlimit conversion between host and target.

linux-user: rlimit conversion between host and target.

rlim_t conversion between host and target added.
Otherwise there are some incorrect case like
- RLIM_INFINITY on 32bit target -> 64bit host.
- RLIM_INFINITY on 64bit host -> mips and sparc target ?
- Big value(for 32bit target) on 64bit host -> 32bit target.

One is added into getrlimit, setrlimit, and ugetrlimit. It converts both
RLIM_INFINITY and value bigger than target can hold(>31bit) to RLIM_INFINITY.

Another one is added to guest_stack_size calculation introduced by
703e0e89. The rule is mostly same except the result on the case is keeping
the value of guest_stack_size.

Slightly tested for SH4, and x86_64 -linux-user on x86_64-pc-linux host.

Signed-off-by: Takashi YOSHII <takasi-y@ops.dti.ne.jp>
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>