elfutils: Add run-backtrace-{native|data}.sh to known failures

elfutils: Add run-backtrace-{native|data}.sh to known failures

musl's thread startup/teardown sequences and frame-pointer handling
differ from glibc. elfutils can fail to terminate unwinds properly
in multithreaded musl apps which leads to truncated or bogus traces
and then the test's "must contain main" assertion fails.

Skip this test on musl systems

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>