Hardcodes Linux as the platform for the NDK crosstool unit tests because that's what the test data is based on. Fixes #581.

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MOS_MIGRATED_REVID=107687820

Author: ahumesky

src/test/java/com/google/devtools/build/lib/bazel/rules/android/ndkcrosstools/AndroidNdkCrosstoolsTest.java

@@ -61,7 +61,8 @@ public class AndroidNdkCrosstoolsTest {
   static {
     try {
 
-      String hostPlatform = AndroidNdkCrosstools.getHostPlatform(NDK_RELEASE);
+      // NDK test data is based on the x86 64-bit Linux Android NDK.
+      String hostPlatform = "linux-x86_64";
       NdkPaths ndkPaths = new NdkPaths(
           REPOSITORY_NAME,
           hostPlatform,