perf tools: Fix build by checking if extra warnings are supported

The -Wstack-protector and -Wvolatile-register-var warnings, for
instance, are not supported by gcc 3.4.6.

So fix by doing the same check we already do for -fstack-protector-all.

With this and the other patches in this series, perf builds unmodified
on, for instance, RHEL4.

Cc: Eric Dumazet <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Tom Zanussi <[email protected]>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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