[perfetto] Handle hyphens in header guards.
[perfetto] Handle hyphens in header guards.

Turns hyphens into underscores in C++ header guards,
which prevents build failures when generating buildflags files
in directory structures that contain a hyphen.

Test: builds successfully on Fuchsia
Change-Id: I61f5d8de436ced1e01696cf9ed7f1a8609668be3

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto