perf trace: Add conditional define for AT_FDCWD

This one was only defined if _GNU_SOURCE was set in older glibc
versions, check that and provide the define in such cases.

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-ilsgsysr6s3mru7rf2befnu5@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -334,6 +334,10 @@ static size_t syscall_arg__scnprintf_fd(char *bf, size_t size,
 
 #define SCA_FD syscall_arg__scnprintf_fd
 
+#ifndef AT_FDCWD
+#define AT_FDCWD	-100
+#endif
+
 static size_t syscall_arg__scnprintf_fd_at(char *bf, size_t size,
 					   struct syscall_arg *arg)
 {