android: Use gold in arm64 builds too.

Reduces hot-cache link time from 49s to 23s (gcc) and binary size from 72M to
67M (gcc)  -- faster links and a 5MB smaller binary.

(With clang, it's 36s to 19.5s and 75M to 69M.)

It also makes the chrome/android/arm64 config more similar to most other build
configs.

We used to not use this because of
https://sourceware.org/bugzilla/show_bug.cgi?id=18348 , but the gold binary
in NDK r12b (which we currently use) has the flags added in the patches on
that bug, so it should be fine now.

BUG=481855

Review-Url: https://codereview.chromium.org/2410233002
Cr-Original-Commit-Position: refs/heads/master@{#424747}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a4baf802f3058b66976a2085278f13ab3bcd8092

config/compiler/compiler.gni

@@ -78,7 +78,7 @@ declare_args() {
              ((is_linux && (current_cpu == "x64" || current_cpu == "x86" ||
                             current_cpu == "arm" || current_cpu == "mipsel")) ||
               (is_android && (current_cpu == "x86" || current_cpu == "x64" ||
-                              current_cpu == "arm")))
+                              current_cpu == "arm" || current_cpu == "arm64")))
 }
 
 # If it wasn't manually set, set to an appropriate default.