Allow for 32-bit VTS builds

In 32-bit builds a `long` may be 32 bits, but the `long` values on an
AIDL interface are 64 bits.  Therefore need to use `int64_t` for the
corresponding C++ type, not `long`.

Bug: 271056044
Test: VtsAidlKeyMintTargetTest --gtest_filter="*AuthTest*" (32-b)
Change-Id: I19f5a1d825dfcc45087534bbd4239a13cdfec3f7
diff --git a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
index a6a9df6..3c753d1 100644
--- a/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
+++ b/security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
@@ -356,7 +356,7 @@
     SecurityLevel securityLevel_;
     string name_;
     string author_;
-    long challenge_;
+    int64_t challenge_;
 
   private:
     void CheckEncryptOneByteAtATime(BlockMode block_mode, const int block_size,