objtool: Make unreachable annotation inline asms explicitly volatile

Add 'volatile' to the unreachable annotation macro inline asm
statements.  They're already implicitly volatile because they don't have
output constraints, but it's clearer and more robust to make them
explicitly volatile.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/28659257b7a6adf4a7f65920dad70b2b0226e996.1509974104.git.jpoimboe@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/compiler.h

@@ -193,16 +193,16 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  * unique, to convince GCC not to merge duplicate inline asm statements.
  */
 #define annotate_reachable() ({						\
-	asm("%c0:\n\t"							\
-	    ".pushsection .discard.reachable\n\t"			\
-	    ".long %c0b - .\n\t"					\
-	    ".popsection\n\t" : : "i" (__COUNTER__));			\
+	asm volatile("%c0:\n\t"						\
+		     ".pushsection .discard.reachable\n\t"		\
+		     ".long %c0b - .\n\t"				\
+		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
 #define annotate_unreachable() ({					\
-	asm("%c0:\n\t"							\
-	    ".pushsection .discard.unreachable\n\t"			\
-	    ".long %c0b - .\n\t"					\
-	    ".popsection\n\t" : : "i" (__COUNTER__));			\
+	asm volatile("%c0:\n\t"						\
+		     ".pushsection .discard.unreachable\n\t"		\
+		     ".long %c0b - .\n\t"				\
+		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
 #define ASM_UNREACHABLE							\
 	"999:\n\t"							\