linux-user/sparc: Don't zero high half of PC, NPC, PSR in sigreturn

linux-user/sparc: Don't zero high half of PC, NPC, PSR in sigreturn

The function do_sigreturn() tries to store the PC, NPC and PSR in
uint32_t local variables, which implicitly drops the high half of
these fields for 64-bit guests.

The usual effect was that a guest which used signals would crash on
return from a signal unless it was lucky enough to take it while the
PC was in the low 4GB of the address space.  In particular, Debian
/bin/dash and /bin/bash would segfault after executing external
commands.

Use abi_ulong, which is the type these fields all have in the
__siginfo_t struct.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201105212314.9628-4-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>