Fix build with new googletest

The new googletest requires prefix to be non-empty.

Exempt-From-Owner-Approval: fix test
Change-Id: Ic039cb657b455919e429a3ec2107893b1734e8a1
diff --git a/libunwindstack/tests/ArmExidxDecodeTest.cpp b/libunwindstack/tests/ArmExidxDecodeTest.cpp
index 7b1dd92..69a7816 100644
--- a/libunwindstack/tests/ArmExidxDecodeTest.cpp
+++ b/libunwindstack/tests/ArmExidxDecodeTest.cpp
@@ -1662,7 +1662,7 @@
   ASSERT_EQ(0x10U, (*exidx_->regs())[15]);
 }
 
-INSTANTIATE_TEST_SUITE_P(, ArmExidxDecodeTest,
+INSTANTIATE_TEST_SUITE_P(Unwindstack, ArmExidxDecodeTest,
                          ::testing::Values("logging", "register_logging", "no_logging"));
 
 }  // namespace unwindstack