Add staticcheck tool

vendor/honnef.co/go/tools/lintcmd/cache/UPSTREAM

@@ -0,0 +1,10 @@
+This package is a copy of cmd/go/internal/cache.
+
+Differences from upstream:
+- we continue to use renameio instead of lockedfile for writing trim.txt
+- we still use I/O helpers that work with earlier versions of Go.
+- we use a cache directory specific to Staticcheck
+- we use a Staticcheck-specific salt
+
+The last upstream commit we've looked at was:
+06ac303f6a14b133254f757e54599c48e3c2a4ad