um/x86: Add system call table to header file

The generic system call tracing infrastructure requires access to the
system call table. The symbol is already visible to the linker but is
lacking a public declaration.

Add a public declaration.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://patch.msgid.link/20250703-uml-have_syscall_tracepoints-v1-1-23c1d3808578@linutronix.de
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: t-8ch

arch/x86/um/asm/syscall.h

@@ -9,6 +9,8 @@ typedef asmlinkage long (*sys_call_ptr_t)(unsigned long, unsigned long,
 					  unsigned long, unsigned long,
 					  unsigned long, unsigned long);
 
+extern const sys_call_ptr_t sys_call_table[];
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #ifdef CONFIG_X86_32