main: use TARGET_ARCH only for the target-specific #define

main: use TARGET_ARCH only for the target-specific #define

Everything else needs to match the executable name, which is
TARGET_NAME.

Before:
    $ sh4eb-linux-user/qemu-sh4eb --help
    usage: qemu-sh4 [options] program [arguments...]
    Linux CPU emulator (compiled for sh4 emulation)

After:
    $ sh4eb-linux-user/qemu-sh4eb --help
    usage: qemu-sh4eb [options] program [arguments...]
    Linux CPU emulator (compiled for sh4eb emulation)

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1370349928-20419-5-git-send-email-pbonzini@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>