perf tools: Move barrier() definition to tools/include/linux/compiler.h

To make it generally accessible by other tools/ projects, also will be
used in the tools/arch/*/include/asm/barrier.h files that are being
introduced now.

Cc: Adrian Hunter <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Don Zickus <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/include/linux/compiler.h

···
 #ifndef _TOOLS_LINUX_COMPILER_H_
 #define _TOOLS_LINUX_COMPILER_H_
 
+/* Optimization barrier */
+/* The "volatile" is due to gcc bugs */
+#define barrier() __asm__ __volatile__("": : :"memory")
+
 #ifndef __always_inline
 # define __always_inline	inline __attribute__((always_inline))
 #endif

tools/perf/perf-sys.h

···
 #define CPUINFO_PROC    {"model name"}
 #endif
 
-#define barrier() asm volatile ("" ::: "memory")
-
 #ifndef cpu_relax
 #define cpu_relax() barrier()
 #endif