Override vcvars options

Author: zooba

windows-release/openssl-build.yml

@@ -21,7 +21,7 @@ parameters:
 - name: VCVarsOptions
   displayName: 'vcvarsall.bat options'
   type: string
-  default: ''
+  required: false
 - name: IncludeX86
   displayName: 'Include x86'
   type: boolean