Add to makefile: "make fix-tests" to fix failing tests.

The last change to flags detection caused a bunch of tests to fail.
The reason is that they are bogus, all recent Intel chips don't have
RDTSCP indicated in the test files, whereas they have it in reality.
I figured it will be easier to add "--fix" option to run_tests.py,
rather than fixing each testfile by hand.

This is also extended in the Makefile:

"make test" runs the tests and reports discrepancies.
"make fix-tests" fixes any offending tests. This blindly assumes that
libcpuid is sane.
Fix broken tests, where rdtscp in recent Intel chips is missing.

As described in previous commit.