Port S32A_opaque blit row to SkOpts.

This should be a pixel-for-pixel (i.e. bug-for-bug) port.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1820313002
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1820313002
diff --git a/src/core/SkOpts.h b/src/core/SkOpts.h
index 42c47a5..3989047 100644
--- a/src/core/SkOpts.h
+++ b/src/core/SkOpts.h
@@ -39,6 +39,7 @@
 
     extern void (*blit_mask_d32_a8)(SkPMColor*, size_t, const SkAlpha*, size_t, SkColor, int, int);
     extern void (*blit_row_color32)(SkPMColor*, const SkPMColor*, int, SkPMColor);
+    extern void (*blit_row_s32a_opaque)(SkPMColor*, const SkPMColor*, int, U8CPU);
 
     // This function is an optimized version of SkColorCubeFilter::filterSpan
     extern void (*color_cube_filter_span)(const SkPMColor[],