Specify SONAME when building Rust shared libs.

Without specifying -soname, cc binaries are unable to locate Rust
provided shared libraries. This adds the -soname linker flag for shared
libraries.

Bug: 158490355
Test: readelf -d <cc_binary> shows the expected SONAME
Change-Id: I66852a7ce24d5ea5e426f11bc1834fb56a150628

rust/library_test.go

@@ -114,3 +114,17 @@ func TestValidateLibraryStem(t *testing.T) {
 			}`)
 
 }
+
+func TestSharedLibraryFlags(t *testing.T) {
+	ctx := testRust(t, `
+		rust_library_host {
+			name: "libfoo",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+		}`)
+
+	libfooShared := ctx.ModuleForTests("libfoo", "linux_glibc_x86_64_shared").Output("libfoo.so")
+	if !strings.Contains(libfooShared.Args["linkFlags"], "-Wl,-soname=libfoo.so") {
+		t.Errorf("missing expected -Wl,-soname linker flag for libfoo shared lib, linkFlags: %#v", libfooShared.Args["linkFlags"])
+	}
+}