multibuild openblas when USE=int64 is specified.
multibuild lapack-reference when USE=int64 and/or USE=static is specified.
Thanks to sfabbro: dodoc should be outside the function, they do not change
multilib as well for openblas
openblas: Strip the _int64 suffix from the BUILD_VARIANT to calculate the ABI
multilib as well for lapack-reference