Fix hwloc build for non x86 platforms

Commit a6bf9c84 yesterday triggered the building of hwloc in TensorFlow.
While many platforms (windows, mac, android) were excluded from building
hwloc, others like ppc64le and raspberry pi still tried to build hwloc.

This fails because hwloc references x86 specific files. Instead of excluding
those platforms from building with hwloc, lets add conditions to only include
the x86 files during a build on the x86 platform. This might enable the
other platforms to still take advantage of hwloc function.