x86: Fix build regression with CONFIG_KEXEC_JUMP enabled

Build 6.13-rc12 for x86_64 with gcc 14.2.1 fails with the error:

  ld: vmlinux.o: in function `virtual_mapped':
  linux/arch/x86/kernel/relocate_kernel_64.S:249:(.text+0x5915b): undefined reference to `saved_context_gdt_desc'

when CONFIG_KEXEC_JUMP is enabled.

This was introduced by commit 07fa619 ("x86/kexec: Restore GDT on
return from ::preserve_context kexec") which introduced a use of
saved_context_gdt_desc without a declaration for it.

Fix that by including asm/asm-offsets.h where saved_context_gdt_desc
is defined (indirectly in include/generated/asm-offsets.h which
asm/asm-offsets.h includes).

Fixes: 07fa619 ("x86/kexec: Restore GDT on return from ::preserve_context kexec")
Signed-off-by: Damien Le Moal <[email protected]>
Acked-by: Borislav Petkov (AMD) <[email protected]>
Acked-by: David Woodhouse <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Linus Torvalds <[email protected]>

Author: damien-lemoal

arch/x86/kernel/relocate_kernel_64.S

@@ -13,6 +13,7 @@
 #include <asm/pgtable_types.h>
 #include <asm/nospec-branch.h>
 #include <asm/unwind_hints.h>
+#include <asm/asm-offsets.h>
 
 /*
  * Must be relocatable PIC code callable as a C function, in particular