cargo kcov seem to lose the target list upon reruns

[lu-zero]

I wanted to run it on --release binaries and they failed with

     Running "kcov" "--exclude-pattern=aom_build" "/usr/src/rav1e/target/cov/rav1e-8585560a084273d8" "/usr/src/rav1e/target/release/deps/rav1e-8585560a084273d8"

running 33 tests
kcov: Process exited with signal 4 (SIGILL) at 0x7ffff722f003

kcov: Illegal instructions are sometimes caused by some GCC versions
kcov: miscompiling C++ headers. If the problem is persistent, try running
kcov: with --verify. For more information, see
kcov: http://github.com/SimonKagstrom/kcov/issues/18

trying to run it again leads to

    Coverage found the following executables: []
     Running "kcov" "--merge" "--exclude-pattern=aom_build" "/usr/src/rav1e/target/cov"

[richardwhiuk]

I dug into this - it's caused by rust-lang/cargo#3530