This CL adds configs for the arm64 and x64 fuchsia
device targets, sets up the necessary linker flags,
and disables some functionality that is not currently
supported on Fuchsia.
Bug: 119831161
Test: Compile walleye, internal validation against
fuchsia_arm64-eng and fuchsia_x86_64-eng.
Change-Id: I2881b99d2e3a1995e2d8c00a2d86ee101a972c94
