fix llvm intrinsic function for pow, powi

[KristofferC]

Fixes a test error as shown in https://s3.amazonaws.com/julialang-reports/nanosoldier/pkgeval/by_hash/c6440b9_vs_d0156b5/SIMD.primary.log

[codecov-commenter]

Codecov Report

Base: 90.46% // Head: 90.46% // No change to project coverage 👍

Coverage data is based on head (5e0ec9a) compared to base (c919181).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #100   +/-   ##
=======================================
  Coverage   90.46%   90.46%           
=======================================
  Files           3        3           
  Lines         514      514           
=======================================
  Hits          465      465           
  Misses         49       49           

Impacted Files	Coverage Δ
src/LLVM_intrinsics.jl	97.95% <100.00%> (ø)

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