Enable signing Windows builds with SHA1 environment variable (GH-11279)

(cherry picked from commit d3bbc5241363d5fa4e749fe509c97c12501ae966)

Co-authored-by: Steve Dower <steve.dower@microsoft.com>
diff --git a/PCbuild/pyproject.props b/PCbuild/pyproject.props
index 6d36977..2019ca8 100644
--- a/PCbuild/pyproject.props
+++ b/PCbuild/pyproject.props
@@ -185,10 +185,11 @@
     <SdkBinPath Condition="!Exists($(SdkBinPath))">$(registry:HKEY_LOCAL_MACHINE\Software\Microsoft\Windows Kits\Installed Roots@KitsRoot)\bin\x86</SdkBinPath>
     <SdkBinPath Condition="!Exists($(SdkBinPath))">$(registry:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SDKs\Windows\v7.1A@InstallationFolder)\Bin\</SdkBinPath>
     <_SignCommand Condition="Exists($(SdkBinPath)) and '$(SigningCertificate)' != '' and $(SupportSigning)">"$(SdkBinPath)\signtool.exe" sign /q /a /n "$(SigningCertificate)" /fd sha256 /t http://timestamp.verisign.com/scripts/timestamp.dll /d "Python $(PythonVersion)"</_SignCommand>
+    <_SignCommand Condition="Exists($(SdkBinPath)) and '$(SigningCertificateSha1)' != '' and $(SupportSigning)">"$(SdkBinPath)\signtool.exe" sign /q /a /sha1 "$(SigningCertificateSha1)" /fd sha256 /t http://timestamp.verisign.com/scripts/timestamp.dll /d "Python $(PythonVersion)"</_SignCommand>
     <_MakeCatCommand Condition="Exists($(SdkBinPath))">"$(SdkBinPath)\makecat.exe"</_MakeCatCommand>
   </PropertyGroup>
-  
-  <Target Name="_SignBuild" AfterTargets="AfterBuild" Condition="'$(SigningCertificate)' != '' and $(SupportSigning)">
+
+  <Target Name="_SignBuild" AfterTargets="AfterBuild" Condition="'$(_SignCommand)' != '' and $(SupportSigning)">
     <Error Text="Unable to locate signtool.exe. Set /p:SignToolPath and rebuild" Condition="'$(_SignCommand)' == ''" />
     <Exec Command='$(_SignCommand) "$(TargetPath)" || $(_SignCommand) "$(TargetPath)" || $(_SignCommand) "$(TargetPath)"' ContinueOnError="false" />
   </Target>