x86_64 is used as a baseline: the "x86_64" entry, whatever status it has,
is transformed into "all", and then the other entries in ARCHITECTURES
either dropped or rearranged appropriately.
Note that this recipe depends in on an older version of binutils
(2.26.1), as the current version of binutils (version 2.28.1) has ld
crash in linking the libLTO.so library from the bundled llvm. This is,
by the way, the same on the recipe of llvm-3.8.1 in this repository.