Small optimization for the CI pipeline. (#15088)

* azure-pipelines: cache csources to speed up build

Building csources takes about 2-4 mins, and since it hasn't changed for
a long time, employ some caching to cut the time spent.

* azure-pipelines: remove ppa avoidance configs

Testing shows that there aren't any difference between having this and
not having it, so removing this to simplify the code.

(cherry picked from commit c292c57e48)

azure-pipelines.yml

@@ -42,9 +42,10 @@ steps:
     condition: eq(variables['Agent.OS'], 'Windows_NT')
 
   - checkout: self
+    fetchDepth: 1
 
-  - bash: git clone --depth 1 https://github.com/nim-lang/csources.git
-    displayName: 'Checkout csources'
+  - bash: git clone --depth 1 https://github.com/nim-lang/csources
+    displayName: 'Checkout Nim csources'
 
   - task: NodeTool@0
     inputs:
@@ -62,19 +63,13 @@ steps:
   - bash: |
       sudo dpkg --add-architecture i386
 
-      # Downgrade llvm, libgcc and libstdc++:
+      # Downgrade llvm:
       # - llvm has to be downgraded to have 32bit version installed for sfml.
-      # - libgcc and libstdc++ have to be downgraded as an optimization to
-      #   prevent the use of the toolchain ppa, which has a terrible download
-      #   speed.
       cat << EOF | sudo tee /etc/apt/preferences.d/pin-to-rel
-      Package: libllvm6.0 libgcc1 libstdc++6
+      Package: libllvm6.0
       Pin: origin "azure.archive.ubuntu.com"
       Pin-Priority: 1001
 
-      Package: *
-      Pin: release o=LP-PPA-ubuntu-toolchain-r-test
-      Pin-Priority: 100
       EOF
 
       sudo apt-fast update -qq
@@ -128,8 +123,19 @@ steps:
       make -v
     displayName: 'System information'
 
+  - bash: echo '##vso[task.setvariable variable=csources_version]'"$(git -C csources rev-parse HEAD)"
+    displayName: 'Get csources version'
+
+  - task: Cache@2
+    inputs:
+      key: 'csources | "$(Agent.OS)" | $(CPU) | $(csources_version)'
+      path: csources/bin
+    displayName: 'Restore built csources'
+
+
   - bash: |
       ncpu=
+      ext=
       case '$(Agent.OS)' in
       'Linux')
         ncpu=$(nproc)
@@ -139,19 +145,24 @@ steps:
         ;;
       'Windows_NT')
         ncpu=$NUMBER_OF_PROCESSORS
+        ext=.exe
         ;;
       esac
       [[ -z "$ncpu" || $ncpu -le 0 ]] && ncpu=1
 
-      make -C csources -j $ncpu CC=gcc ucpu=$(CPU)
-    displayName: 'Build csources'
+      if [[ -x csources/bin/nim$ext ]]; then
+        echo "Found cached compiler, skipping build"
+      else
+        make -C csources -j $ncpu CC=gcc ucpu=$(CPU) koch=no
+      fi
+      cp csources/bin/nim$ext bin
+    displayName: 'Build 1-stage compiler from csources'
 
   - bash: nim c koch
     displayName: 'Build koch'
 
     # set result to omit the "bash exited with error code '1'" message
-  - bash: |
-      ./koch runCI || echo '##vso[task.complete result=Failed]'
+  - bash: ./koch runCI || echo '##vso[task.complete result=Failed]'
     displayName: 'Run CI'
     env:
       SYSTEM_ACCESSTOKEN: $(System.AccessToken)