Since we introduced $GARBLE_DIR, we stopped recommending the use of
toolexec directly. It's still possible to set up the right flags and env
vars, but that will be a moving target.
In particular, string obfuscation in #16 will require using $GARBLE_DIR
in more scenarios. A work-in-progress patch for string obfuscation
triggered this test script to start failing for the reason above.
While at it, we don't care about what the second build contains, since
we already compare it with the previous build.
The problem with the "grep" built-in command is that it prints the
entire data if there is an error. We don't want megabytes of binary
output for a test.