x86/percpu: Avoid sparse warning with cast to named address space

Teach sparse about __seg_fs and __seg_gs named address space
qualifiers to to avoid warnings about unexpected keyword at
the end of cast operator.

Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231204210320.114429-3-ubizjak@gmail.com
Closes: https://lore.kernel.org/oe-kbuild-all/202310080853.UhMe5iWa-lkp@intel.com/

Author: ubizjak

arch/x86/include/asm/percpu.h

@@ -36,6 +36,11 @@
 
 #ifdef CONFIG_CC_HAS_NAMED_AS
 
+#ifdef __CHECKER__
+#define __seg_gs		__attribute__((address_space(__seg_gs)))
+#define __seg_fs		__attribute__((address_space(__seg_fs)))
+#endif
+
 #ifdef CONFIG_X86_64
 #define __percpu_seg_override	__seg_gs
 #else