ci: split install-msys2 step into two separate scripts

src/ci/azure-pipelines/steps/run.yml

@@ -98,6 +98,13 @@ steps:
   displayName: Install msys2
   condition: and(succeeded(), not(variables.SKIP_JOB))
 
+- bash: src/ci/scripts/install-msys2-packages.sh
+  env:
+    AGENT_OS: $(Agent.OS)
+    SYSTEM_WORKFOLDER: $(System.Workfolder)
+  displayName: Install msys2 packages
+  condition: and(succeeded(), not(variables.SKIP_JOB))
+
 - bash: src/ci/scripts/install-mingw.sh
   env:
     AGENT_OS: $(Agent.OS)

src/ci/scripts/install-msys2-packages.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if isWindows; then
+    pacman -S --noconfirm --needed base-devel ca-certificates make diffutils tar
+
+    # FIXME(#65767): workaround msys bug, step 2
+    arch=i686
+    if [ "$MSYS_BITS" = "64" ]; then
+      arch=x86_64
+    fi
+    pacman -U --noconfirm --noprogressbar mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
+    rm mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
+
+    # Make sure we use the native python interpreter instead of some msys equivalent
+    # one way or another. The msys interpreters seem to have weird path conversions
+    # baked in which break LLVM's build system one way or another, so let's use the
+    # native version which keeps everything as native as possible.
+    cp C:/Python27amd64/python.exe C:/Python27amd64/python2.7.exe
+    ciCommandAddPath "C:\\Python27amd64"
+fi

src/ci/scripts/install-msys2.sh

@@ -23,18 +23,4 @@ if isWindows; then
     mkdir -p "${SYSTEM_WORKFOLDER}/msys2/home/${USERNAME}"
 
     ciCommandAddPath "${SYSTEM_WORKFOLDER}/msys2/usr/bin"
-    export PATH="${SYSTEM_WORKFOLDER}/msys2/usr/bin:${PATH}"
-
-    pacman -S --noconfirm --needed base-devel ca-certificates make diffutils tar
-
-    # FIXME(#65767): workaround msys bug, step 2
-    pacman -U --noconfirm --noprogressbar mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
-    rm mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
-
-    # Make sure we use the native python interpreter instead of some msys equivalent
-    # one way or another. The msys interpreters seem to have weird path conversions
-    # baked in which break LLVM's build system one way or another, so let's use the
-    # native version which keeps everything as native as possible.
-    cp C:/Python27amd64/python.exe C:/Python27amd64/python2.7.exe
-    ciCommandAddPath "C:\\Python27amd64"
 fi