Revert "ci/win: don't use lastexitcode hack on mingw build"

This reverts commit bc43d2559f.

stderr redirection should make the workaround work for mingw builds.

ci/build.ps1

@@ -97,21 +97,15 @@ bin\nvim --version ; exitIfFailed
 
 # Functional tests
 # The $LastExitCode from MSBuild can't be trusted
-if ($compiler -eq 'MSVC') {
-  $failed = $false
-  # Temporarily turn off tracing to reduce log file output
-  Set-PSDebug -Off
-  cmake --build . --config $cmakeBuildType --target functionaltest -- $cmakeGeneratorArgs |
-    foreach { $failed = $failed -or
-      $_ -match 'Running functional tests failed with error'; $_ }
-  Set-PSDebug -Trace 1
-  if ($failed) {
-    exit $LastExitCode
-  }
-}
-else {
-  cmake --build . --config $cmakeBuildType --target functionaltest -- $cmakeGeneratorArgs
-  exitIfFailed
+$failed = $false
+# Temporarily turn off tracing to reduce log file output
+Set-PSDebug -Off
+cmake --build . --config $cmakeBuildType --target functionaltest -- $cmakeGeneratorArgs |
+  foreach { $failed = $failed -or
+    $_ -match 'Running functional tests failed with error'; $_ }
+Set-PSDebug -Trace 1
+if ($failed) {
+  exit $LastExitCode
 }