Use structs for texture intrinsic return types.

[maleadt]

Intrinsic has incorrect return type!
[4 x float] (i64, float)* @llvm.nvvm.tex.unified.1d.v4f32.f32
in function _Z37julia_kernel_texture_warp_native_502613CuDeviceArrayI7Float32Li1ELi1EE15CuDeviceTextureIS0_Li1E11ArrayMemoryLifalseE16NearestNeighbourE

[codecov]

Codecov Report

Merging #554 (4d3018d) into master (434324b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #554   +/-   ##
=======================================
  Coverage   77.95%   77.95%           
=======================================
  Files         116      116           
  Lines        6424     6424           
=======================================
  Hits         5008     5008           
  Misses       1416     1416           

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