x86, tracing: add notrace to asm-x86/linkage.h

notrace signals that a function should not be traced. Most of the
time this is used by tracers to annotate code that cannot be
traced - it's in a volatile state (such as in user vdso context
or NMI context) or it's in the tracer internals.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/asm-x86/linkage.h

 #ifndef __ASM_LINKAGE_H
 #define __ASM_LINKAGE_H
 
+#undef notrace
+#define notrace __attribute__((no_instrument_function))
+
 #ifdef CONFIG_X86_64
 #define __ALIGN .p2align 4,,15
 #define __ALIGN_STR ".p2align 4,,15"