Make libhidl_gtest_helper host_supported

Bug: N/A
Test: mma
Change-Id: I36843804d836c04f667d1fdb2b3ff20555408bc5

Android.bp

diff --git a/Android.bp b/Android.bp
index 82413b9..9d268f6 100644
--- a/Android.bp
+++ b/Android.bp
@@ -48,6 +48,7 @@
 
 cc_library_headers {
     name: "libhidl_gtest_helper",
+    host_supported: true,
     export_include_dirs: ["gtest_helper"],
 }