x32: make X32, !IA32_EMULATION setups able to execute x32 binaries

It's really trivial - the only wrinkle is making sure that
compiler knows that ia32-related side of COMPAT_ARCH_DLINFO
is dead code on such configs (we don't get there without
having passed compat_elf_check_arch(), and on such configs
that'll fail for ia32 binary).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/Kconfig

@@ -2864,7 +2864,6 @@ config IA32_EMULATION
 	depends on X86_64
 	select ARCH_WANT_OLD_COMPAT_IPC
 	select BINFMT_ELF
-	select COMPAT_BINFMT_ELF
 	select COMPAT_OLD_SIGACTION
 	help
 	  Include code to run legacy 32-bit programs under a
@@ -2900,6 +2899,7 @@ config COMPAT_32
 config COMPAT
 	def_bool y
 	depends on IA32_EMULATION || X86_X32
+	select COMPAT_BINFMT_ELF if BINFMT_ELF
 
 if COMPAT
 config COMPAT_FOR_U64_ALIGNMENT

arch/x86/include/asm/elf.h

@@ -364,7 +364,7 @@ do {									\
 #define COMPAT_ARCH_DLINFO						\
 if (exec->e_machine == EM_X86_64)					\
 	ARCH_DLINFO_X32;						\
-else									\
+else if (IS_ENABLED(CONFIG_IA32_EMULATION))				\
 	ARCH_DLINFO_IA32
 
 #define COMPAT_ELF_ET_DYN_BASE	(TASK_UNMAPPED_BASE + 0x1000000)