Merge pull request #5 from dart-lang/zanderso-patch-2

Pass a -march flag for arm64 clang build
diff --git a/BUILD.gn b/BUILD.gn
index d9f5160..a9b4a50 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -42,13 +42,14 @@
   defines = []
   sources = []
   include_dirs = [ "src/include" ]
+  asmflags = []
 
   if ((current_cpu == "arm" || current_cpu == "arm64") && is_android && is_clang) {
     # Disable the integrated assembler and use the one shipped with the NDK.
     import("//build/config/android/config.gni")
     rebased_android_toolchain_root =
         rebase_path(android_toolchain_root, root_build_dir)
-    asmflags = [
+    asmflags += [
       "-fno-integrated-as",
       "-B${rebased_android_toolchain_root}/bin",
     ]
@@ -79,6 +80,7 @@
     sources += crypto_sources_linux_arm
   } else if (current_cpu == "arm64" && (is_linux || is_android)) {
     sources += crypto_sources_linux_aarch64
+    asmflags += [ "-march=armv8-a+crypto" ]
   } else {
     public_configs = [ ":no_asm_config" ]
   }