build: comparison tool NPE fix

This should fix the spurious comparison tool failures.
See discussion here: https://github.com/bitcoin/bitcoin/pull/6305

The race fix was cherry-picked on top of the version we're currently using, so
it should be functionally identical otherwise.

depends/packages/native_comparisontool.mk

@@ -1,8 +1,8 @@
 package=native_comparisontool
-$(package)_version=be0eef7
+$(package)_version=8c6666f
 $(package)_download_path=https://github.com/theuni/bitcoind-comparisontool/raw/master
 $(package)_file_name=pull-tests-$($(package)_version).jar
-$(package)_sha256_hash=46c2efa25e717751e1ef380d428761b1e37b43d6d1e92ac761b15ee92703e560
+$(package)_sha256_hash=a865332b3827abcde684ab79f5f43c083b0b6a4c97ff5508c79f29fee24f11cd
 $(package)_install_dirname=BitcoindComparisonTool_jar
 $(package)_install_filename=BitcoindComparisonTool.jar