Teach x-ci-accept-failures to Windows CI tests

.github/workflows/windows.yml

@@ -106,6 +106,7 @@ jobs:
       - name: Install packages
         env:
           ALL_CHANGED_PACKAGES: ${{ steps.changed-packages.outputs.data }}
+          WINDOWSENV: ${{ matrix.windows_env }}
         if: github.event_name != 'push'
         run: |
           $pkgs = $env:ALL_CHANGED_PACKAGES | ConvertFrom-Json
@@ -119,7 +120,23 @@ jobs:
               0 { Write-Host "`e[1;32m$pkg installed successfully`e[0m."; Break }
               5 { Write-Host "$pkg is not installable. `e[1;33mSkip`e[0m."; Break } # TODO: Remove when https://github.com/ocaml/opam/issues/6017 is fixed
               20 { Write-Host "$pkg is not installable. `e[1;33mSkip`e[0m."; Break }
-              31 { Write-Host "`e[1;31m$pkg failed to build`e[0m."; $failed = $true; Break }
+              31 {
+                $unexpected = $true
+                Foreach ($failpkg in Get-ChildItem -Path $env:OPAMROOT\default\.opam-switch\build -Name) {
+                  if (opam show -f x-ci-accept-failures: "$failpkg" | Select-String -Pattern """$env:WINDOWSENV""" -SimpleMatch) {
+                    $unexpected = $false
+                    Write-Host "$failpkg failed to build but that was expected:"
+                    Write-Host "its 'x-ci-accept-failures' field contains ""$env:WINDOWSENV"". `e[1;33mSkip`e[0m."
+                  } else {
+                    Write-Host "`e[1;31m$failpkg failed to build`e[0m."
+                  }
+                }
+                Remove-Item -Path $env:OPAMROOT\default\.opam-switch\build -Recurse -Force
+                if ($unexpected) {
+                  $failed = $true
+                }
+                Break
+              }
               default { throw "Unexpected error $_" }
             }
             Write-Host

packages/conf-aarch64-linux-gnu-gcc/conf-aarch64-linux-gnu-gcc.1/opam

@@ -20,3 +20,4 @@ Please install aarch64-linux-gnu-gcc manually, as there is no known package
 for it for your distribution."""
     {failure}
 x-maintenance-intent: ["(latest)"]
+x-ci-accept-failures: ["cygwin" "msys2"]

packages/conf-x86_64-linux-gnu-gcc/conf-x86_64-linux-gnu-gcc.1/opam

@@ -20,3 +20,4 @@ Please install x86_64-linux-gnu-gcc manually, as there is no known package
 for it for your distribution."""
     {failure}
 x-maintenance-intent: ["(latest)"]
+x-ci-accept-failures: ["cygwintypo" "msys2"]