x86/elf: Use e_machine to choose DLINFO in compat

Since TIF_X32 is going away, avoid using it to find the ELF type on
ARCH_DLINFO.

According to SysV AMD64 ABI Draft, an AMD64 ELF object using ILP32 must
have ELFCLASS32 with (E_MACHINE == EM_X86_64), so use that ELF field to
differentiate a x32 object from a IA32 object when loading ARCH_DLINFO in
compat mode.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20201004032536.1229030-5-krisman@collabora.com

arch/x86/include/asm/elf.h

@@ -361,7 +361,7 @@ do {									\
 #define AT_SYSINFO		32
 
 #define COMPAT_ARCH_DLINFO						\
-if (test_thread_flag(TIF_X32))						\
+if (exec->e_machine == EM_X86_64)					\
 	ARCH_DLINFO_X32;						\
 else									\
 	ARCH_DLINFO_IA32