Kernel/LibC: Rework userspace syscall interface

Kernel syscall API no longer zeros all unused argument registers and
libc now uses inlined syscall macro internally. This significantly
cleans up generated code for basic syscall wrapper functions.

userspace/programs/DynamicLoader/utils.h

@@ -1,10 +1,18 @@
 #pragma once
 
 #include <BAN/Traits.h>
+
+#include <unistd.h> // make sure syscall function is declared before defining it
+
+#include <errno.h>
 #include <kernel/API/Syscall.h>
 
-#include <stddef.h>
-#include <stdint.h>
+#define syscall(...) ({ \
+		long _ret = -ERESTART; \
+		while (_ret == -ERESTART) \
+			_ret = _kas_syscall(__VA_ARGS__); \
+		_ret; \
+	})
 
 template<typename T>
 inline constexpr T min(T a, T b)
@@ -18,12 +26,6 @@ inline constexpr T max(T a, T b)
 	return a > b ? a : b;
 }
 
-template<typename... Ts> requires (sizeof...(Ts) <= 5) && ((BAN::is_integral_v<Ts> || BAN::is_pointer_v<Ts>) && ...)
-inline auto syscall(long syscall, Ts... args)
-{
-	return Kernel::syscall(syscall, (uintptr_t)args...);
-}
-
 void print(int fd, const char* buffer);
 
 [[noreturn]] void print_error_and_exit(const char* message, int error);