Add post about changes to x.py defaults

posts/inside-rust/2020-08-12-changes-to-x-py-defaults.md

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+---
+layout: post
+title: "Changes to x.py defaults"
+author: Joshua Nelson
+team: the compiler team <https://www.rust-lang.org/governance/teams/compiler>
+---
+
+Recently, the defaults for [x.py] - the tool used to [bootstrap] the rust compiler from source - changed. If you regularly contribute to the rust compiler, this might affect your workflow.
+
+## What changes were made?
+
+- The default stage is now dependent on the subcommand.
+  + `dist`: stage 2
+  + `build`: stage 1
+  + `test`: stage 1
+  + `doc`: stage 0
+
+- stage1 rustc artifacts are no longer built by `x.py build --stage 1`. To get the old behavior back, use `x.py build --stage 1 src/rustc`.
+
+- `debuginfo` now defaults to `1` when `debug = true`. Previously, the default was 2.
+
+## Why were the changes made?
+
+For a detailed rationale of the changes, as well as more information about the alternatives considered, see
+
+- [the MCP]
+- the [implementation PR]
+- the [Zulip stream]
+
+[x.py]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html#what-is-xpy
+[bootstrap]: https://rustc-dev-guide.rust-lang.org/building/bootstrapping.html
+[the MCP]: https://github.com/rust-lang/compiler-team/issues/326
+[implementation PR]: https://github.com/rust-lang/rust/pull/73964
+[Zulip stream]: https://rust-lang.zulipchat.com/#narrow/stream/233931-xxx/topic/Use.20sane.20defaults.20in.20x.py.20compiler-team.23326