perf trace: Avoid compile error wrt redefining bool

Make part of an existing TODO conditional to avoid the following build
error:
```
tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c:26:14: error: cannot combine with previous 'char' declaration specifier
   26 | typedef char bool;
      |              ^
include/stdbool.h:20:14: note: expanded from macro 'bool'
   20 | #define bool _Bool
      |              ^
tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c:26:1: error: typedef requires a name [-Werror,-Wmissing-declarations]
   26 | typedef char bool;
      | ^~~~~~~~~~~~~~~~~
2 errors generated.
```

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230913184957.230076-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c

@@ -23,7 +23,9 @@
 #define MAX_CPUS  4096
 
 // FIXME: These should come from system headers
+#ifndef bool
 typedef char bool;
+#endif
 typedef int pid_t;
 typedef long long int __s64;
 typedef __s64 time64_t;