Add libc++abi darwin file group

This commit adds `libc++abi_darwin` file group because `libc++.1.dylib`
depends on `libc++abi.1.dylib`.

Bug: 111579848
Test: prebuilts/clang-tools/build-prebuilts.sh
Test: out/soong/dist/bin/header-abi-dumper --help
Change-Id: I453166991bc64974e5978af4200e899912b5f4d9
diff --git a/Android.bp b/Android.bp
index 6cd85b4..e339c7c 100644
--- a/Android.bp
+++ b/Android.bp
@@ -25,9 +25,13 @@
 }
 
 llvm_darwin_filegroup {
-    name: "libclang_darwin",
+    name: "libclang_cxx_darwin",
 }
 
 llvm_darwin_filegroup {
     name: "libc++_darwin",
 }
+
+llvm_darwin_filegroup {
+    name: "libc++abi_darwin",
+}