x86/percpu: Enable named address spaces for all capable GCC versions

Enable named address spaces also for GCC 6, GCC 7 and GCC 8
releases. These compilers all produce kernel images that boot
without problems.

Use compile-time test to detect compiler support for named
address spaces. The test passes with GCC 6 as the earliest
compiler version where the support for named address spaces
was introduced.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240520082134.121320-1-ubizjak@gmail.com

Author: ubizjak

arch/x86/Kconfig

@@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
 endmenu
 
 config CC_HAS_NAMED_AS
-	def_bool CC_IS_GCC && GCC_VERSION >= 90100
+	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
+	depends on CC_IS_GCC
 
 config CC_HAS_NAMED_AS_FIXED_SANITIZERS
 	def_bool CC_IS_GCC && GCC_VERSION >= 130300