This can be used to run tests multple times, with e.g. differing
QEMU settings, by adding something like this to the FATE configuration
file:

    target_exec="qemu-aarch64-static"
    fate_targets="fate-checkasm fate-cpu"

    fate_environments="sve128 sve256 sve512"
    sve128_env="QEMU_CPU=max,sve128=on"
    sve256_env="QEMU_CPU=max,sve256=on"
    sve512_env="QEMU_CPU=max,sve512=on"

It's also possible to customize the target_exec command further
by injecting a sufficiently quoted variable into it, which then can
be updated for each run, e.g. target_exec="\$(CUR_EXEC_CMD)".

For each of the environment names in fate_environments, the tests
that are run get the name suffixed on the fate tests in the
test log and fate report, e.g. "fate-checkasm-h264dsp_sve128".
Signed-off-by: Martin Storsjö <martin@martin.st>