Switch NDK libc++ from prebuilts/ndk to prebuilts/clang

Remove old NDK libc++ Soong modules, and use libunwind instead of
ndk_libunwind.

Bug: http://b/332594828
Test: m nothing --no-skip-soong-tests
Test: m blueprint_tests
Change-Id: I6763a4dbba660240e47a4a2eb179382c0a0a9840

cc/cc_test.go

@@ -2760,7 +2760,7 @@ func TestIncludeDirectoryOrdering(t *testing.T) {
 		"external/foo/libarm",
 		"external/foo/lib32",
 		"external/foo/libandroid_arm",
-		"defaults/cc/common/ndk_libc++_shared",
+		"defaults/cc/common/ndk_libc++_shared_include_dirs",
 	}
 
 	conly := []string{"-fPIC", "${config.CommonGlobalConlyflags}"}