Merge pull request #479 from Microsoft/detect_os

Changing to a more reliable way to detect os for build

Author: littleaj

core/build.gradle

@@ -24,7 +24,10 @@ plugins {
 
 apply from: "$buildScriptsDir/common-java.gradle"
 apply from: "$buildScriptsDir/publishing.gradle"
-if (System.env."windir" != null) {
+
+import org.apache.tools.ant.taskdefs.condition.Os
+
+if (Os.isFamily(Os.FAMILY_WINDOWS)) {
     apply from: "native.gradle"
 } else {
     logger.warn("Native binaries build is only supported on Windows systems; native components will not be built.")