kernel: Move the signal handling logic to after a syscall sets its return value

When a signal was caught after a syscall, it was doing so without preserving the return value of the syscall.

kernel/src/arch/x86_64/CPU.cpp

@@ -186,6 +186,7 @@ extern "C" void arch_interrupt_entry(Registers* regs)
     {
         SyscallArgs args = { regs->rdi, regs->rsi, regs->rdx, regs->r10, regs->r8, regs->r9 };
         regs->rax = (u64)invoke_syscall(regs, args, regs->rax);
+        Scheduler::current()->process_pending_signals(regs);
     }
     else
     {

kernel/src/sys/Syscall.cpp

@@ -15,8 +15,6 @@ i64 invoke_syscall(Registers* regs, SyscallArgs args, u64 syscall)
 
     auto rc = syscalls[syscall](regs, args);
 
-    Scheduler::current()->process_pending_signals(regs);
-
     if (rc.has_error()) return -rc.error();
     return (i64)rc.value();
 }