[PATCH v4 0/6] Travis jobs for linux with musl libc

Cc: Junio C Hamano <gitster@pobox.com>,
 SZEDER Gábor <szeder.dev@gmail.com>,
 Eric Sunshine <sunshine@sunshineco.com>,
 Johannes Schindelin <johannes.schindelin@gmx.de>

Recently, we've un-broken git for Linux with musl libc, and we have a serie to fix false negative with busybox shell utils.

Add a CI job on Travis and Azure to make sure we won't break it again.

Change from v3:
* reword 2/6: adding su behavior in util-linux and busybox
* 6/6: Drop change to azure-pipelines.yml, and declare this series will
  be used for Travis only. Since Azure will be replaced by GitHub Action
  in a later series.

Hi Junio, The series for GitHub Actions will need to be rebased on this series again. 6/6 in that seriess will have UD conflicts. Please "git rm azure-pipelines.yml" to fix conflicts.

SZEDER Gábor (1):
  ci: make MAKEFLAGS available inside the Docker container in the
    Linux32 job

Đoàn Trần Công Danh (5):
  ci/lib-docker: preserve required environment variables
  ci/linux32: parameterise command to switch arch
  ci: refactor docker runner script
  ci/linux32: libify install-dependencies step
  travis: build and test on Linux with musl libc and busybox

 .travis.yml                                   | 10 ++++-
 azure-pipelines.yml                           |  4 +-
 ci/install-docker-dependencies.sh             | 18 +++++++++
 ci/lib.sh                                     |  8 ++++
 ...n-linux32-build.sh => run-docker-build.sh} | 39 +++++++++++++------
 ci/{run-linux32-docker.sh => run-docker.sh}   | 28 ++++++++++---
 6 files changed, 86 insertions(+), 21 deletions(-)
 create mode 100755 ci/install-docker-dependencies.sh
 rename ci/{run-linux32-build.sh => run-docker-build.sh} (63%)
 rename ci/{run-linux32-docker.sh => run-docker.sh} (43%)

Range-diff against v3:
1:  2fdce60075 = 1:  2fdce60075 ci: make MAKEFLAGS available inside the Docker container in the Linux32 job
2:  b7b079f559 ! 2:  db574b3ff9 ci/lib-docker: preserve required environment variables
    @@ Commit message
     
         We're using "su -m" to preserve environment variables in the shell run
         by "su". But, that options will be ignored while "-l" (aka "--login") is
    -    specified.
    +    specified in util-linux and busybox's su.
    +
    +    In a later patch this script will be reused for checking Git for Linux
    +    with musl libc on Alpine Linux, Alpine Linux uses "su" from busybox.
     
         Since we don't have interest in all environment variables,
         pass only those necessary variables to the inner script.
3:  8c8cf3eb24 = 3:  a13715245f ci/linux32: parameterise command to switch arch
4:  22cc7960c3 = 4:  b5de868c1e ci: refactor docker runner script
5:  2e0d54f81e = 5:  c39451ffe5 ci/linux32: libify install-dependencies step
6:  b61ed50cf6 ! 6:  231affae83 travis: build and test on Linux with musl libc and busybox
    @@ .travis.yml: matrix:
            os: linux
            compiler:
     
    - ## azure-pipelines.yml ##
    -@@ azure-pipelines.yml: jobs:
    -       PathtoPublish: t/failed-test-artifacts
    -       ArtifactName: failed-test-artifacts
    - 
    -+- job: linux_musl
    -+  displayName: linux-musl
    -+  condition: succeeded()
    -+  pool:
    -+    vmImage: ubuntu-latest
    -+  steps:
    -+  - bash: |
    -+       test "$GITFILESHAREPWD" = '$(gitfileshare.pwd)' || ci/mount-fileshare.sh //gitfileshare.file.core.windows.net/test-cache gitfileshare "$GITFILESHAREPWD" "$HOME/test-cache" || exit 1
    -+
    -+       res=0
    -+       sudo AGENT_OS="$AGENT_OS" BUILD_BUILDNUMBER="$BUILD_BUILDNUMBER" BUILD_REPOSITORY_URI="$BUILD_REPOSITORY_URI" BUILD_SOURCEBRANCH="$BUILD_SOURCEBRANCH" BUILD_SOURCEVERSION="$BUILD_SOURCEVERSION" SYSTEM_PHASENAME="$SYSTEM_PHASENAME" SYSTEM_TASKDEFINITIONSURI="$SYSTEM_TASKDEFINITIONSURI" SYSTEM_TEAMPROJECT="$SYSTEM_TEAMPROJECT" CC=$CC MAKEFLAGS="$MAKEFLAGS" jobname=linux-musl bash -lxc ci/run-docker.sh || res=1
    -+
    -+       sudo chmod a+r t/out/TEST-*.xml
    -+       test ! -d t/failed-test-artifacts || sudo chmod a+r t/failed-test-artifacts
    -+
    -+       test "$GITFILESHAREPWD" = '$(gitfileshare.pwd)' || sudo umount "$HOME/test-cache" || res=1
    -+       exit $res
    -+    displayName: 'jobname=linux-musl ci/run-docker.sh'
    -+    env:
    -+      GITFILESHAREPWD: $(gitfileshare.pwd)
    -+  - task: PublishTestResults@2
    -+    displayName: 'Publish Test Results **/TEST-*.xml'
    -+    inputs:
    -+      mergeTestResults: true
    -+      testRunTitle: 'musl'
    -+      platform: Linux
    -+      publishRunAttachments: false
    -+    condition: succeededOrFailed()
    -+  - task: PublishBuildArtifacts@1
    -+    displayName: 'Publish trash directories of failed tests'
    -+    condition: failed()
    -+    inputs:
    -+      PathtoPublish: t/failed-test-artifacts
    -+      ArtifactName: failed-test-artifacts
    -+
    - - job: static_analysis
    -   displayName: StaticAnalysis
    -   condition: succeeded()
    -
      ## ci/install-docker-dependencies.sh ##
     @@ ci/install-docker-dependencies.sh: Linux32)
      			libssl-dev libexpat-dev gettext python >/dev/null