fix gcc.avx512 builds

Clang was not affected because of the special Clang case at 88:

  #elif defined(__clang__)
      return __builtin_convertvector(v, D);

Change-Id: I9165ded1befdd221ce06d86b9c57589f934ae9ac
Reviewed-on: https://skia-review.googlesource.com/145734
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
1 file changed