perf tools: Introduce weak alternative to sched_getcpu()

Which is just a wrapper for sys_getcpu and is not present in at least
musl libc.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-kblef7svmhr0g93kkx78envg@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/arch/x86/include/asm/unistd_32.h

@@ -7,3 +7,6 @@
 #ifndef __NR_gettid
 # define __NR_gettid 224
 #endif
+#ifndef __NR_getcpu
+# define __NR_getcpu 318
+#endif

tools/arch/x86/include/asm/unistd_64.h

@@ -7,3 +7,6 @@
 #ifndef __NR_gettid
 # define __NR_gettid 186
 #endif
+#ifndef __NR_getcpu
+# define __NR_getcpu 309
+#endif