Link device binaries dynamically by default.

Device binaries currently are linked statically by default. Instead we
should be linking these dynamic by default. To avoid conflicts when
manually specifying rlib dependencies on modules, we always link libstd
dynamically for all device modules except static libraries.

This removes the "prefer_dynamic" property entirely to avoid confusion.

Bug: 165161105
Test: m profcollectd is built dynamically.
Test: cd external/rust/; mma
Test: cd external/crosvm/; mma
Change-Id: I25ac897040acbcc2d97c791a33e8e01610632272

rust/compiler_test.go

@@ -177,3 +177,30 @@ func TestLints(t *testing.T) {
 		})
 	}
 }
+
+// Test that devices are linking the stdlib dynamically
+func TestStdDeviceLinkage(t *testing.T) {
+	ctx := testRust(t, `
+		rust_binary {
+			name: "fizz",
+			srcs: ["foo.rs"],
+		}
+		rust_library {
+			name: "libfoo",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+		}`)
+	fizz := ctx.ModuleForTests("fizz", "android_arm64_armv8-a").Module().(*Module)
+	fooRlib := ctx.ModuleForTests("libfoo", "android_arm64_armv8-a_rlib").Module().(*Module)
+	fooDylib := ctx.ModuleForTests("libfoo", "android_arm64_armv8-a_dylib").Module().(*Module)
+
+	if !android.InList("libstd", fizz.Properties.AndroidMkDylibs) {
+		t.Errorf("libstd is not linked dynamically for device binaries")
+	}
+	if !android.InList("libstd", fooRlib.Properties.AndroidMkDylibs) {
+		t.Errorf("libstd is not linked dynamically for rlibs")
+	}
+	if !android.InList("libstd", fooDylib.Properties.AndroidMkDylibs) {
+		t.Errorf("libstd is not linked dynamically for dylibs")
+	}
+}