Build with devtoolset-7 on aarch64 as well as 32-bit ARM. Upstream refuses
to build HotSpot on aarch64 with GCC < 5 (JDK-8360869), and el7 ships GCC
4.8.5, so the aarch64 build failed in configure. The devtoolset-7 machinery
was already present but gated on %{arm}, which does not cover aarch64.