Remove bashisms from scripts

[ "a" == "b" ] is a bashism, the portable alternative is [ "a" = "b" ].

Fixes the following issue on Debian where /bin/sh == dash:

    # ./build-lima-memtester-static-binary.sh
    ./build-lima-memtester-static-binary.sh: 3: [: x: unexpected operator
    ./build-lima-memtester-static-binary.sh: 11: ./build-lima-memtester-static-binary.sh: -DHAVE_NO_LIBMALI_BLOB: not found

The alternative would be to explicitly use #!/bin/bash in the script but since
the fix is trivial we might as well make it.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>