[simd_ops] Build tests with -fpic

[ostannard]

Summary

Since https://reviews.llvm.org/rG2047c10c22b0, the dso_local specifier
must be included in IR when building non-PIC code. The bitcode files in
this test suite do not have this, so will only work when all of the code
is built with -fpic.

The alternative to this would be to re-generate the bitcode with the
dso_local specifier where needed, but I don't know how this code was
generated in the first place, and don't want to modify the bitcode files
in-place if they might be later re-generated.

[MaskRay]

We may have to reinstate the dso_local specifier for ELF definitions it it turns out to be widespread issues, but adding this LG.

[asbirlea]

I'll look into regenerating the bitcode files, but in the mean time this looks good.

[ostannard]

Committed as 224328460d75e1fa16a23901b3aa494b89e0a842.

Bitcode/simd_ops/CMakeLists.txt

     ${CMAKE_CURRENT_SOURCE_DIR}/${ARCH}_scalar_tests/scalar_${namebc}.bc
   )
   target_link_libraries(simd_ops_${namebc} simd_ops)
+  set_property(TARGET simd_ops_${namebc} PROPERTY POSITION_INDEPENDENT_CODE ON)
 endforeach()