x86/orc: Make the is_callthunk() definition depend on CONFIG_BPF_JIT=y

Recent commit:

  02012623 Revert "x86/orc: Make it callthunk aware"

Made the only user of is_callthunk() depend on CONFIG_BPF_JIT=y, while
the definition of the helper function is unconditional.

Move is_callthunk() inside the #ifdef block.

Addresses this build failure:

   arch/x86/kernel/callthunks.c:296:13: error: ‘is_callthunk’ defined but not used [-Werror=unused-function]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>

arch/x86/kernel/callthunks.c

@@ -293,6 +293,7 @@ void *callthunks_translate_call_dest(void *dest)
 	return target ? : dest;
 }
 
+#ifdef CONFIG_BPF_JIT
 static bool is_callthunk(void *addr)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
@@ -306,7 +307,6 @@ static bool is_callthunk(void *addr)
 	return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);
 }
 
-#ifdef CONFIG_BPF_JIT
 int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;