Merge branch 'test_progs-asan'

Andrii Nakryiko says:

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Add necessary infra to build selftests with ASAN (or any other sanitizer). Fix
a bunch of found memory leaks and other memory access issues.

v1->v2:
  - don't add ASAN flavor, but allow extra flags for build (Alexei);
  - fix few more found issues, which somehow were missed first time.
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Signed-off-by: Alexei Starovoitov <ast@kernel.org>