internal/syscall/unix: use getrandom_linux_generic.go on arm64be

Change-Id: I259c0a4c3ef1e157f467d52861cf80f0d18a7607
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/215342
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/go/internal/syscall/unix/getrandom_linux_generic.go b/libgo/go/internal/syscall/unix/getrandom_linux_generic.go
index 95748d5..0c79ae5 100644
--- a/libgo/go/internal/syscall/unix/getrandom_linux_generic.go
+++ b/libgo/go/internal/syscall/unix/getrandom_linux_generic.go
@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux
-// +build arm64 nios2 riscv64
+// +build arm64 arm64be nios2 riscv64
 
 package unix