* build: update-external-binaries fetches sccache
* build: add util.add_exec_bit in scripts/
* build: use util.add_exec_bit in create-dist
* build: use util.add_exec_bit in update-external-binaries
this is needed to work around a bug in python's zipfile module that doesn't preserve the exec bit
https://bugs.python.org/issue18262
* fix: linting errors
* build: vsts, circleci use patched sccache
* build: always look for the x64 sccache
as it's the only arch we have it on
* fix: windows-specific errors in updaste-external-binaries
* fix: tyop
* fix: set SCCACHE_BUCKET, SCCACHE_TWO_TIER on circleci
* fix: syntax error in circleci yaml
* fix: keep churning
* chore: add tracer to file downloader
* docs: add sccache instructions for GN builds
* build: pull down the darwin sccache on mas builds
* build: use gn sync verbosely on circleci and vsts
* docs: copyediting
* build: remove unnecessary cache-dir arg
* docs: fix shell quoting in gn build instructions
* fix: invoke gclient without -verbose in circleci
* refactor: remove debug tracer
* fix: invoke gclient without -verbose in appveyor
* fix: invoke gclient without -verbose in vsts
* fix: pull add_exec_bit from correct source
* fix: remove 'SCCACHE_TWO_TIER' from CI scripts
* refactor: remove SCCACHE_BUCKET from ci scripts
this environment variable will be set via the CI UI instead
* refactor: clarify log message
* fix: set SCCACHE_PATH correctly for Windows CI
e315e4d308