linux-user: Implement capability prctls

This is PR_CAPBSET_READ, PR_CAPBSET_DROP and the "legacy"
PR_CAP_AMBIENT PR_GET_SECUREBITS, PR_SET_SECUREBITS.

All of these arguments are integer values only, and do not
require mapping of values between host and guest.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220106225738.103012-5-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/syscall.c

@@ -6504,10 +6504,15 @@ static abi_long do_prctl(CPUArchState *env, abi_long option, abi_long arg2,
     case PR_SET_UNALIGN:
         return do_prctl_set_unalign(env, arg2);
 
+    case PR_CAP_AMBIENT:
+    case PR_CAPBSET_READ:
+    case PR_CAPBSET_DROP:
     case PR_GET_DUMPABLE:
     case PR_SET_DUMPABLE:
     case PR_GET_KEEPCAPS:
     case PR_SET_KEEPCAPS:
+    case PR_GET_SECUREBITS:
+    case PR_SET_SECUREBITS:
     case PR_GET_TIMING:
     case PR_SET_TIMING:
     case PR_GET_TIMERSLACK: