Rollup of 20 pull requests

[frewsxcv]

• Successful merges: Expand documentation of process::exit and exec #38518, Support unprivileged symlink creation in Windows #38921, Add 128-bit atomics #38959, Add peek APIs to std::net #38983, Add warning for () to ! switch #39009, branchless .filter(_).count() #39107, Tell emscripten to remove exception handling code when panic=abort #39193, Provide Entry-like API for Option #39289, Fix full path being output with rustdoc -h #39312, Check for correct env keys in Command #39338, Fix a few impl stability attributes #39393, Expand derive macros in the MacroExpander #39442, Don't suggest to use things which weren't found either #39443, save-analysis: be more paranoid about generated paths #39453, Change tracking issue for proc_macro feature to #38356 #39454, Fix bootstrap.py issues with new rustbuild build system (fixes #39469) #39471, Add a name for the parameter to TryFrom::try_from. #39477, rustbuild: Add x.py to source tarballs #39478, README path correction #39527, correct version in which more_struct_aliases was/will be stable #39552
• Failed merges:

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @sfackler (or someone else) soon.

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[frewsxcv]

@bors r+ p=50

[bors]

📌 Commit 1d6ab05 has been approved by frewsxcv

[bors]

⌛ Testing commit 1d6ab05 with merge ee6b2cc...

[bors]

💔 Test failed - status-appveyor