Export libclang-cpp.dylib

Bug: http://b/150809112

... and stop exporting libLLVM, libclang, and libclang_cxx.
libclang-cpp is a new upstream library exports both the clang and LLVM
C++ symbols and can replace libLLVM and (android-toolchain-only)
libclang_cxx.so.

Test: build go/ab/aosp-clang-tools and run them.
Change-Id: I81afc9d622210e9a3e5841e51e5fc9ef66707a0e
diff --git a/Android.bp b/Android.bp
index 0b2f808..2dea64d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -57,11 +57,7 @@
 }
 
 llvm_darwin_filegroup {
-    name: "libLLVM_darwin",
-}
-
-llvm_darwin_filegroup {
-    name: "libclang_cxx_darwin",
+    name: "libclang-cpp_darwin",
 }
 
 llvm_darwin_filegroup {
@@ -71,7 +67,3 @@
 llvm_darwin_filegroup {
     name: "libc++abi_darwin",
 }
-
-llvm_darwin_filegroup {
-    name: "libxml2_darwin",
-}