Need a workaround of a rare kcov bug that showed up in CI Nightly (kcov: warning: Other status: 0x85).

[DamrongGuoy]

We got a rare issue with KCov.

We got a nightly CI failure: https://drake-cdash.csail.mit.edu/test/156381170 in //multibody/plant:multibody_plant_scalar_conversion_test of linux-bionic-clang-bazel-nightly-coverage/871.

The sign of the bug is:

kcov: warning: Other status: 0x85

This command (thanks to @jeremyma-tri ) reproduced the problem on my Ubuntu 18.04.

env CC=clang-9 CXX=clang++-9 bazel  test --compilation_mode=dbg --config=kcov //multibody/plant:multibody_plant_scalar_conversion_test

with error message:

FAIL: //multibody/plant:multibody_plant_scalar_conversion_test (see /home/damrongguoy/.cache/bazel/_bazel_damrongguoy/ae8964252cc8671edabcee844c1a72e5/execroot/drake/bazel-out/k8-dbg/testlogs/multibody/plant/multibody_plant_scalar_conversion_test/test.log)
INFO: From Testing //multibody/plant:multibody_plant_scalar_conversion_test:
==================== Test output for //multibody/plant:multibody_plant_scalar_conversion_test:
kcov: warning: Other status: 0x85

kcov: 531 invalid breakpoints skipped in /home/damrongguoy/.cache/bazel/_bazel_damrongguoy/ae8964252cc8671edabcee844c1a72e5/execroot/drake/bazel-out/k8-dbg/bin/multibody/plant/multibody_plant_scalar_conversion_test
kcov: 9 invalid breakpoints skipped in /lib/x86_64-linux-gnu/libc.so.6

It is the same thing as Drake issue #14424 that @ggould-tri fixed by PR #14425. The underlying cause is this KCov issue SimonKagstrom/kcov#339.

The workaround is to change the unit test in a trivial way just to get a different object code.

Assign to @joemasterjohn . Thank you.