std: Remove internal definitions of cfg_if! macro

[alexcrichton]

This is duplicated in a few locations throughout the sysroot to work
around issues with not exporting a macro in libstd but still wanting it
available to sysroot crates to define blocks. Nowadays though we can
simply depend on the cfg-if crate on crates.io, allowing us to use it
from there!

[rust-highfive]

r? @bluss

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[alexcrichton]

Note that this is here because there's usage of a bare cfg_if! macro invocation in stdsimd. That needs to be updated to cfg_if::cfg_if! before this can be removed, but that can hopefully happen in parallel with this.

[alexcrichton]

r? @sfackler

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:1792cf4d:start=1560180228390210893,finish=1560180229177715781,duration=787504888
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
travis_time:start:test_codegen
Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:02:59] 
[01:02:59] running 144 tests
[01:03:02] i..iii.....iii...iiii....i......................i..i.................i.....i..........ii.i..i..i.ii. 100/144
[01:03:04] test result: ok. 114 passed; 0 failed; 30 ignored; 0 measured; 0 filtered out
[01:03:04] 
[01:03:04]  finished in 4.505
[01:03:04] travis_fold:end:test_codegen
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travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:03:06] 
[01:03:06] running 9 tests
[01:03:06] iiiiiiiii
[01:03:06] 
[01:03:06]  finished in 0.147
[01:03:06] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-gdb+lldb (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:03:21] 
[01:03:21] running 122 tests
[01:03:46] .iiiii...i.....i..i...i..i.i.i..i.ii..i.i.....i..i....i..........iiii..........i...ii...i.......ii.i 100/122
[01:03:50] .i.i......iii.i.....ii
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[01:03:50]  finished in 28.999
[01:03:50] travis_fold:end:test_debuginfo

---
[01:19:38] 
[01:19:38] To learn more, run the command again with --verbose.
[01:19:38] 
[01:19:38] 
[01:19:38] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace compiler-builtins-c" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "std" "--" "--quiet"
[01:19:38] 
[01:19:38] 
[01:19:38] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:19:38] Build completed unsuccessfully in 1:15:43
---
166968 ./obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps
156504 ./src/llvm-project/clang
150572 ./obj/build/bootstrap/debug/incremental
135300 ./obj/build/bootstrap/debug/incremental/bootstrap-oxgzobynhmm1
135296 ./obj/build/bootstrap/debug/incremental/bootstrap-oxgzobynhmm1/s-fd1cypvdk7-ynen56-19ca4iajxr4qm
125304 ./obj/build/x86_64-unknown-linux-gnu/test/mir-opt
123656 ./src/llvm-project/llvm/test/CodeGen
117304 ./obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib
117248 ./obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[sfackler]

@bors r+

[bors]

📌 Commit 8eb7f36 has been approved by sfackler

[RalfJung]

@alexcrichton any idea why this might break building libstd with xargo?

    Updating crates.io index
   Compiling core v0.0.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/libcore)
   Compiling compiler_builtins v0.1.16
   Compiling cc v1.0.37
   Compiling libc v0.2.58
   Compiling build_helper v0.1.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/build_helper)
   Compiling unwind v0.0.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/libunwind)
   Compiling cfg-if v0.1.9
error[E0463]: can't find crate for `core`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0463`.
error: Could not compile `cfg-if`.
warning: build failed, waiting for other jobs to finish...
error: build failed
error: `"cargo" "build" "--release" "--manifest-path" "/tmp/xargo.EVc4fCLCAwza/Cargo.toml" "--target" "x86_64-unknown-linux-gnu" "-p" "std"` failed with exit code: Some(101)

[RalfJung]

Shouldn't this enable the rustc-dep-of-std feature?

[RalfJung]

Hm, that leads to a build failure?!?

error: failed to select a version for `cfg-if`.
    ... required by package `std v0.0.0 (/home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd)`
    ... which is depended on by `sysroot v0.0.0 (/tmp/xargo.NWDhLbN6RoeP)`
versions that meet the requirements `^0.1.9` are: 0.1.9

the package `std` depends on `cfg-if`, with features: `rustc-dep-of-std` but `cfg-if` does not have these features.


failed to select a version for `cfg-if` which could resolve this conflict

But the feature is present since rust-lang/cfg-if@3e31141.

[RalfJung]

Looks like the crates.io version differs from the GH version in that parts of the toml are commented out...??

# [dependencies]
# core = { version = "1.0.0", optional = true, package = 'rustc-std-workspace-core' }
# compiler_builtins = { version = '0.1.2', optional = true }
#
# [features]
# rustc-dep-of-std = ['core', 'compiler_builtins']

[RalfJung]

Reported as rust-lang/cfg-if#22.

[RalfJung]

And submitted hopefully fixing PR as #61828.