Commits on Apr 1, 2020

1. Add support for -Cembed-bitcode=no …

   This commit is the Cargo half of support necessary for
   rust-lang/rust#70458. Today the compiler emits embedded bytecode in
   rlibs by default, but compresses it. This is both extraneous disk space
   and wasted build time for almost all builds, so the PR in question there
   is changing rustc to have a `-Cembed-bitcode` flag which, when enabled,
   places the bitcode in the object file rather than an auxiliary file (no
   extra compression), but also enables `-Cembed-bitcode=no` to disable
   bitcode emission entirely.
   
   This Cargo support changes Cargo to pass `-Cembed-bitcode=no` for almost
   all compilations. Cargo will keep `lto = true` and such working by not
   passing this flag (and thus allowing bitcode to get embedded), but by
   default `cargo build` and `cargo build --release` will no longer have
   any bitcode in rlibs which should result in speedier builds!
   
   Most of the changes here were around the test suite and various
   assertions about the `rustc` command lines we spit out. One test was
   hard-disabled until we can get `-Cembed-bitcode=no` into nightly, and
   then we can make it a nightly-only test. The test will then be stable
   again once `-Cembed-bitcode=no` hits stable.
   
   Note that this is intended to land before the upstream `-Cembed-bitcode`
   change. The thinking is that we'll land everything in rust-lang/rust all
   at once so there's no build time regressions for anyone. If we were to
   land the `-Cembed-bitcode` PR first then there would be a build time
   regression until we land Cargo changes because rustc would be emitting
   uncompressed bitcode by default and Cargo wouldn't be turning it off.

   

   alexcrichton committed Apr 1, 2020
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