Update Android.bp files to not use test_per_src.

Each rust_test module corresponds to a single test binary now.

Bug: 158500462
Test: Affected test modules build.
Change-Id: Ib6fb6c87ad3093580516724cf6f34c8d29fb220e
diff --git a/Android.bp b/Android.bp
index 240ce06..d948226 100644
--- a/Android.bp
+++ b/Android.bp
@@ -19,15 +19,9 @@
     compile_multilib: "first", // added
 }
 
-rust_test_host {
+rust_defaults {
     name: "proc-macro2_tests",
     crate_name: "proc_macro2",
-    srcs: [
-        "tests/comments.rs",
-        "tests/features.rs",
-        "tests/marker.rs",
-        "tests/test.rs",
-    ],
     test_suites: ["general-tests"],
     auto_gen_config: true,
     edition: "2018",
@@ -47,6 +41,38 @@
 }
 
 rust_test_host {
+    name: "proc-macro2_tests_comments",
+    defaults: ["proc-macro2_tests"],
+    srcs: [
+        "tests/comments.rs",
+    ],
+}
+
+rust_test_host {
+    name: "proc-macro2_tests_features",
+    defaults: ["proc-macro2_tests"],
+    srcs: [
+        "tests/features.rs",
+    ],
+}
+
+rust_test_host {
+    name: "proc-macro2_tests_marker",
+    defaults: ["proc-macro2_tests"],
+    srcs: [
+        "tests/marker.rs",
+    ],
+}
+
+rust_test_host {
+    name: "proc-macro2_tests_test",
+    defaults: ["proc-macro2_tests"],
+    srcs: [
+        "tests/test.rs",
+    ],
+}
+
+rust_test_host {
     name: "proc-macro2_tests_proc_macro2",
     crate_name: "proc_macro2",
     srcs: ["src/lib.rs"],