siginterrupt is obsolete

Summary

siginterrupt is obsolete but is used in rts/posix/Signals.c

Steps to reproduce

> ./validate --legacy
[...]
rts/posix/Signals.c:689:5: error:
     erreur: « siginterrupt » est obsolète: Use sigaction with SA_RESTART instead [-Werror=deprecated-declarations]
      689 |     siginterrupt(SIGINT, 1);    // isn't this the default? --SDM
          |     ^~~~~~~~~~~~
    |
689 |     siginterrupt(SIGINT, 1);    // isn't this the default? --SDM
    |     ^
Dans le fichier inclus depuis rts/posix/Signals.h:12,
                 depuis rts/RtsSignals.h:13,

                 depuis rts/posix/Signals.c:13:0: error: 

/usr/include/signal.h:311:12: error:
     note: déclaré ici
      311 | extern int siginterrupt (int __sig, int __interrupt) __THROW
          |            ^~~~~~~~~~~~
    |
311 | extern int siginterrupt (int __sig, int __interrupt) __THROW
    | 

Environment

• GHC version used: HEAD
• GCC version: 10.2.0

Optional:

• Operating System: Archlinux
• System Architecture: x86-64