Import Wycheproof XChaCha20-Poly1305 tests.

Change-Id: Iaa10ebfc61aa2f928f057a62737d5d97743d6305
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/39187
Reviewed-by: Adam Langley <agl@google.com>

sources.cmake

diff --git a/sources.cmake b/sources.cmake
index c94f9c3..8275233 100644
--- a/sources.cmake
+++ b/sources.cmake
@@ -103,4 +103,5 @@
   third_party/wycheproof_testvectors/rsa_pss_misc_test.txt
   third_party/wycheproof_testvectors/rsa_signature_test.txt
   third_party/wycheproof_testvectors/x25519_test.txt
+  third_party/wycheproof_testvectors/xchacha20_poly1305_test.txt
 )