travis: Add timestamps to all build messages

When debugging why builds are taking so long it's often useful to get the
timestamp of all log messages as we're not always timing every tiny step of the
build. I wrote a [utility] for prepending a relative timestamp from the start of
a process which is now downloaded to the builders and is what we wrap the entire
build invocation in.

[utility]: https://github.com/alexcrichton/stamp-rs

Closes rust-lang#40577

.travis.yml

@@ -53,7 +53,9 @@ matrix:
       osx_image: xcode8.2
       install: &osx_install_sccache >
         travis_retry curl -o /usr/local/bin/sccache https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror/2017-03-16-sccache-x86_64-apple-darwin &&
-          chmod +x /usr/local/bin/sccache
+          chmod +x /usr/local/bin/sccache &&
+        travis_retry curl -o /usr/local/bin/stamp https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror/2017-03-17-stamp-x86_64-apple-darwin &&
+          chmod +x /usr/local/bin/stamp
     - env: >
         RUST_CHECK_TARGET=check
         RUST_CONFIGURE_ARGS=--build=i686-apple-darwin
@@ -118,6 +120,11 @@ env:
     # AWS_SECRET_ACCESS_KEY=...
     - secure: "Pixhh0hXDqGCdOyLtGFjli3J2AtDWIpyb2btIrLe956nCBDRutRoMm6rv5DI9sFZN07Mms7VzNNvhc9wCW1y63JAm414d2Co7Ob8kWMZlz9l9t7ACHuktUiis8yr+S4Quq1Vqd6pqi7pf2J++UxC8R/uLeqVrubzr6+X7AbmEFE="
 
+# Note that this is overridden on OSX builders
+install: >
+  travis_retry curl -o /usr/local/bin/stamp https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror/2017-03-17-stamp-x86_64-unknown-linux-musl &&
+    chmod +x /usr/local/bin/stamp
+
 before_script:
   - >
       echo "#### Disk usage before running script:";
@@ -129,11 +136,11 @@ script:
       if [ "$ALLOW_PR" = "" ] && [ "$TRAVIS_BRANCH" != "auto" ]; then
           echo skipping, not a full build;
       elif [ "$TRAVIS_OS_NAME" = "osx" ]; then
-          travis_retry sh -c 'git submodule deinit -f . && git submodule update --init' &&
-          src/ci/run.sh;
+          travis_retry stamp sh -c 'git submodule deinit -f . && git submodule update --init' &&
+          stamp src/ci/run.sh;
       else
-          travis_retry sh -c 'git submodule deinit -f . && git submodule update --init' &&
-          src/ci/docker/run.sh $IMAGE;
+          travis_retry stamp sh -c 'git submodule deinit -f . && git submodule update --init' &&
+          stamp src/ci/docker/run.sh $IMAGE;
       fi
 
 after_success: