travis: Don't set RUST_LOG globally

I have a suspicion that this caused a large regression in cycle times by forcing
the compiler to perform more checks on every `debug!` statement, so let's test
this out by removing the `RUST_LOG` env var globally.

This regression in cycle time was witnessed between [two] [builds] where the
[PR] in question didn't do much suspicious. Judging by how the stage0 times
*also* regressed though then this is my best guess.

[two]: https://travis-ci.org/rust-lang/rust/builds/210149932
[builds]: https://travis-ci.org/rust-lang/rust/builds/210179995
[PR]: #40446

.travis.yml

@@ -47,7 +47,6 @@ matrix:
         SRC=.
         RUSTC_RETRY_LINKER_ON_SEGFAULT=1
         SCCACHE_ERROR_LOG=/tmp/sccache.log
-        RUST_LOG=sccache=debug
         MACOSX_DEPLOYMENT_TARGET=10.8
         MACOSX_STD_DEPLOYMENT_TARGET=10.7
       os: osx
@@ -61,7 +60,6 @@ matrix:
         SRC=.
         RUSTC_RETRY_LINKER_ON_SEGFAULT=1
         SCCACHE_ERROR_LOG=/tmp/sccache.log
-        RUST_LOG=sccache=debug
         MACOSX_DEPLOYMENT_TARGET=10.8
         MACOSX_STD_DEPLOYMENT_TARGET=10.7
       os: osx
@@ -75,7 +73,6 @@ matrix:
         DEPLOY=1
         RUSTC_RETRY_LINKER_ON_SEGFAULT=1
         SCCACHE_ERROR_LOG=/tmp/sccache.log
-        RUST_LOG=sccache=debug
         MACOSX_DEPLOYMENT_TARGET=10.8
         MACOSX_STD_DEPLOYMENT_TARGET=10.7
       os: osx
@@ -90,7 +87,6 @@ matrix:
         DEPLOY=1
         RUSTC_RETRY_LINKER_ON_SEGFAULT=1
         SCCACHE_ERROR_LOG=/tmp/sccache.log
-        RUST_LOG=sccache=debug
         MACOSX_DEPLOYMENT_TARGET=10.8
         MACOSX_STD_DEPLOYMENT_TARGET=10.7
       os: osx
@@ -109,7 +105,6 @@ matrix:
         DEPLOY_ALT=1
         RUSTC_RETRY_LINKER_ON_SEGFAULT=1
         SCCACHE_ERROR_LOG=/tmp/sccache.log
-        RUST_LOG=sccache=debug
         MACOSX_DEPLOYMENT_TARGET=10.8
         MACOSX_STD_DEPLOYMENT_TARGET=10.7
       os: osx

appveyor.yml

@@ -131,7 +131,6 @@ install:
   - handle.exe -accepteula -help
 
   # Attempt to debug sccache failures
-  - set RUST_LOG=sccache=debug
   - set SCCACHE_ERROR_LOG=%CD%/sccache.log
 
 test_script:

src/bootstrap/native.rs

@@ -18,6 +18,7 @@
 //! LLVM and compiler-rt are essentially just wired up to everything else to
 //! ensure that they're always in place if needed.
 
+use std::env;
 use std::fs::{self, File};
 use std::io::{Read, Write};
 use std::path::Path;
@@ -145,6 +146,10 @@ pub fn llvm(build: &Build, target: &str) {
         cfg.define("CMAKE_CXX_FLAGS", build.cflags(target).join(" "));
     }
 
+    if env::var_os("SCCACHE_ERROR_LOG").is_some() {
+        cfg.env("RUST_LOG", "sccache=debug");
+    }
+
     // FIXME: we don't actually need to build all LLVM tools and all LLVM
     //        libraries here, e.g. we just want a few components and a few
     //        tools. Figure out how to filter them down and only build the right

src/ci/docker/run.sh

@@ -39,7 +39,6 @@ if [ "$SCCACHE_BUCKET" != "" ]; then
     args="$args --env AWS_SECRET_ACCESS_KEY=$AWS_SECRET_ACCESS_KEY"
     args="$args --env SCCACHE_ERROR_LOG=/tmp/sccache/sccache.log"
     args="$args --env SCCACHE_LOG_LEVEL=debug"
-    args="$args --env RUST_LOG=sccache=debug"
     args="$args --volume $objdir/tmp:/tmp/sccache"
 else
     mkdir -p $HOME/.cache/sccache