Enable 64-bit Android Builds

(This is a merge of go/wvgerrit/23686)

This patch removes the makefile lines that previously prevented the
Widevine DRM Plugin from being built as 64-bit on Android. 64-bit
builds are now fully supported.

Only one piece of CDM code has had to change. Due to a bug in
libprotobuf before v3.0, int64 values from protobufs are technically a
different type from int64_t values in code on some 64-bit
architectures. Both have the same in-memory representation at runtime
but are seen as distinct types by the compiler. The compiler will
automatically convert in most places, but template instantiation is
not one of them, so a few places that passed a Protobuf int64 directly
into a template had to be modified.

Please note that tweaks to the mediadrmserver (not covered by this
patch) are needed in order for it to run as 64-bit and load 64-bit DRM
Plugins. Please also note that, as we have no 64-bit L1 OEMCrypto on
any devices, using the 64-bit mediadrmserver and Widevine library will
make your device fall back to L3 for the time being.

Bug: 18949752
Test: OEMCrypto unit tests
Test: Widevine unit tests
Test: Google Play (on Marlin)
Test: Widevine GTS Tests (on Marlin)
Change-Id: Ib6cdf2dd1ff75a1c473cacdc5e22397caa0a656c

libwvdrmengine/cdm/core/test/cdm_engine_test.cpp

@@ -89,8 +89,13 @@ class WvCdmEngineTest : public testing::Test {
     std::string message;
     bool ok = url_request.GetResponse(&message);
     EXPECT_TRUE(ok);
+    // One of many reasons a device might fail to provision is that the server
+    // rejects its keybox.  In that case, we usually see an error of
+    // CERT_PROVISIONING_RESPONSE_ERROR_1.  The error response may help
+    // somebody look through the server logs for more clues.
     ASSERT_EQ(NO_ERROR, cdm_engine_.HandleProvisioningResponse(message, &cert,
-                                                               &wrapped_key));
+                                                               &wrapped_key))
+        << "Error response: " << message;
   }
 
   void GenerateKeyRequest(const std::string& key_id,