A64: Fix some compile errors when building for Android.

src/platform-freebsd.cc

Index: src/platform-freebsd.cc
diff --git a/src/platform-freebsd.cc b/src/platform-freebsd.cc
index c771cd3be029aea168a1333a57a5481690354518..78458a78118eb0469e675eeb7c9b35d2efea6501 100644
--- a/src/platform-freebsd.cc
+++ b/src/platform-freebsd.cc
@@ -189,6 +189,8 @@ void OS::Abort() {
 void OS::DebugBreak() {
 #if (defined(__arm__) || defined(__thumb__))
   asm("bkpt 0");
+#elif defined(__aarch64__)
+  asm("brk 0");
 #else
   asm("int $3");
 #endif