perf tools: Protect header files with a consistent style

There was a colorful mix of header guards - standardize them.

Signed-off-by: John Kacur <jkacur@redhat.com>
LKML-Reference: <alpine.LFD.2.00.0909241756530.11383@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>