perf build: Add make check-headers target

perf build: Add make check-headers target

Don't print header differences during the perf build as it's noisy.
Mostly people won't care and find it annoying.

As it's to improve perf trace beautifier to catch up new changes mostly
in UAPIs, we can make it a separate build target and call it
occasionally.  Make it and build-test related targets phony.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>