x86/bug: Fix old GCC compile fails

For some mysterious reasons the GCC 8 and 9 preprocessor manages to
sporadically fumble _ASM_BYTES(0x0f, 0x0b):

$ grep ".byte[ ]*0x0f" defconfig-build/drivers/net/wireless/realtek/rtlwifi/base.s
        1:       .byte0x0f,0x0b ;
        1:       .byte 0x0f,0x0b ;

which makes the assembler upset and all that. While there are more
_ASM_BYTES() users (notably the NOP instructions), those don't seem
affected. Therefore replace the offending ASM_UD2 with one using the
ud2 mnemonic.

Reported-by: Jean Delvare <[email protected]>
Suggested-by: Uros Bizjak <[email protected]>
Fixes: 85a2d4a ("x86,ibt: Use UDB instead of 0xEA")
Cc: [email protected]
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Peter Zijlstra

arch/x86/include/asm/bug.h

@@ -15,7 +15,7 @@ extern void __WARN_trap(struct bug_entry *bug, ...);
 /*
  * Despite that some emulators terminate on UD2, we use it for WARN().
  */
-#define ASM_UD2		_ASM_BYTES(0x0f, 0x0b)
+#define ASM_UD2		__ASM_FORM(ud2)
 #define INSN_UD2	0x0b0f
 #define LEN_UD2		2