Fix building with clang targeting x86_32 mingw
Fix building with clang targeting x86_32 mingw

In these cases, CLANG_HAS_AVX2 is defined, but _MSC_VER isn't.

The corresponding codepaths are in source/row_win.cc, and the whole
file is guarded with an defined(_MSC_VER).

Change-Id: Idf0cfced3a0ef28c07b1393fe605a904420fd50f
Reviewed-on: https://chromium-review.googlesource.com/983592
Reviewed-by: Frank Barchard <52415189a3f67d375195cbbb6fdb1f1759498e57@chromium.org>
Commit-Queue: Frank Barchard <52415189a3f67d375195cbbb6fdb1f1759498e57@chromium.org>

lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv