Add AArch64 device Rust toolchain.

Bug: 141207434
Test: build example rust device module.
Change-Id: I0932a614942bf4a4d4b6c153fcc4fc79c7f202bd
diff --git a/rust/config/toolchain.go b/rust/config/toolchain.go
index a36d61b..328bca3 100644
--- a/rust/config/toolchain.go
+++ b/rust/config/toolchain.go
@@ -32,6 +32,8 @@
 
 	Is64Bit() bool
 	Supported() bool
+
+	Bionic() bool
 }
 
 type toolchainBase struct {
@@ -53,6 +55,10 @@
 	panic("toolchainBase cannot determine datapath width.")
 }
 
+func (toolchainBase) Bionic() bool {
+	return true
+}
+
 type toolchain64Bit struct {
 	toolchainBase
 }