GitHub Action fixes (#920)

Fix for new GHA 2024.06.10.1.0 runner image behavior which sets env.
vars to empty string, instead of not setting, when build matrix has no
corresponding value.

Workaround 2024.06.03.1.0 GHA runner image bug that continues in
2024.06.10.1.0. Mutex-related SIGSEGVs. See
actions/runner-images#10004.

.github/workflows/windows.yml

@@ -29,6 +29,7 @@ jobs:
     strategy:
       matrix:
         os: [ windows-latest ]
+        generator: [ 'Visual Studio 17 2022' ]
         toolset: [v143, CLangCL]
         arch: [ x64 ]
         check_mkvk: [ NO ]
@@ -254,6 +255,14 @@ jobs:
       if: matrix.check_mkvk == 'ONLY'
       run: scripts/check_mkvk.ps1
 
+    # Works around issues with 2024.06.03.1.0 runner image. See
+    # https://github.com/actions/runner-images/issues/10004 and
+    # https://github.com/actions/runner-images/issues/10055
+    - name: Remove conflicting msvcp140.dll as workaround for runner image bugs.
+      shell: bash -l {0}
+      run: |
+          find "C:/hostedtoolcache/windows/Java_Temurin-Hotspot_jdk" -name "msvcp140.dll" -exec rm {} \;
+
     - name: Test Windows build
       # Tests built for arm64 can't be run as the CI runners are all x64.
       if: matrix.arch == 'x64' && matrix.options.tests == 'ON'

scripts/build_win.ps1

@@ -15,7 +15,7 @@ for ($i=0; $i -lt $args.length; $i++)
 function Set-ConfigVariable {
   param ( $VariableName, $DefaultValue )
   $res = get-variable $VariableName -ValueOnly -ErrorAction 'SilentlyContinue'
-  if ($res -eq $null) {
+  if ([string]::IsNullOrEmpty($res)) {
     $res = [Environment]::GetEnvironmentVariable($VariableName)
     if ($res -eq $null) {
         $res = $DefaultValue