[Metal-Epic:Tools] Compiling Metal 2.0 shaders on XCode 9.3 beta with desktop forward selected fails on iOS

Shaders fail to compile with a series of cube map errors (subset below):

LogShaderCompilers: Warning: 17 Shader compiler errors compiling global shaders for platform SF_METAL_MRT:
  LogShaderCompilers: Warning: /tmp/3733_3798084495.metal(0): Shader VisualizeTexturePSCubeArray, VF None:
   Failed to compile to bytecode locally, code: 1, output:  /tmp/3733_3798084495.metal:49:12: error: no matching function for call to 'sample'
          v8.xyzw = texture_cube_array::sample(VisualizeTextureCubeArray, s0, (v9).xyz, (uint)(v9).w, level(pu_h[1].w));
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~
  /tmp/ue4_stdlib.metal:2141:64: note: candidate template ignored: could not match 'texturecube_array' against 'texture2d_array'
          static inline _attribute_((always_inline)) vec<T, 4> sample(texturecube_array<T, a> tex, sampler s, float3 coord, uint array, bias options)
                                                                 ^
  /tmp/ue4_stdlib.metal:2151:64: note: candidate template ignored: could not match 'texturecube_array' against 'texture2d_array'
          static inline _attribute_((always_inline)) vec<T, 4> sample(texturecube_array<T, a> tex, sampler s, float3 coord, uint array, level options)
                                                                 ^
  /tmp/ue4_stdlib.metal:2161:64: note: candidate template ignored: could not match 'texturecube_array' against 'texture2d_array'
          static inline _attribute_((always_inline)) vec<T, 4> sample(texturecube_array<T, a> tex, sampler s, float3 coord, uint array, gradientcube options)
                                                                 ^
  /tmp/ue4_stdlib.metal:2131:64: note: candidate function template not viable: requires 4 arguments, but 5 were provided
          static inline _attribute_((always_inline)) vec<T, 4> sample(texturecube_array<T, a> tex, sampler s, float3 coord, uint array)
                                                                 ^
  1 error generated.

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