Try fixing unused-variable warnings another way.

If we mark these as extern, the compiler won't complain they're unused.

This is an unsatisfying hack, but last time we tried to condition these
on non-NEON only, Chromium's GN linux ARM bot failed.  They must not be
configured to use the NEON procs?

BUG=skia:4798
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1699473002
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1699473002
diff --git a/src/opts/SkBlitRow_opts_arm.cpp b/src/opts/SkBlitRow_opts_arm.cpp
index 24566ba..d4b1d0d 100644
--- a/src/opts/SkBlitRow_opts_arm.cpp
+++ b/src/opts/SkBlitRow_opts_arm.cpp
@@ -10,15 +10,15 @@
 
 #include "SkBlitRow_opts_arm_neon.h"
 
-static const SkBlitRow::Proc16 sk_blitrow_platform_565_procs_arm[] = {
+extern const SkBlitRow::Proc16 sk_blitrow_platform_565_procs_arm[] = {
     nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
 };
 
-static const SkBlitRow::ColorProc16 sk_blitrow_platform_565_colorprocs_arm[] = {
+extern const SkBlitRow::ColorProc16 sk_blitrow_platform_565_colorprocs_arm[] = {
     nullptr, nullptr,
 };
 
-static const SkBlitRow::Proc32 sk_blitrow_platform_32_procs_arm[] = {
+extern const SkBlitRow::Proc32 sk_blitrow_platform_32_procs_arm[] = {
     nullptr, nullptr, nullptr, nullptr,
 };