linux-user: Support for restarting system calls for SPARC targets

linux-user: Support for restarting system calls for SPARC targets

Update the SPARC main loop and sigreturn code:
 * on TARGET_ERESTARTSYS, wind guest PC backwards to repeat syscall insn
 * set all guest CPU state within signal.c code on sigreturn
 * handle TARGET_QEMU_ESIGRETURN in the main loop as the indication
   that the main loop should not touch any guest CPU state

Signed-off-by: Timothy Edward Baldwin <[email protected]>
Message-id: 1441497448[email protected]
[PMM: Commit message tweaks; drop TARGET_USE_ERESTARTSYS define]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Signed-off-by: Riku Voipio <[email protected]>