Do not dedupe libprotobuf-cpp variants

The vendor variants of libprotobuf-cpp have their version numbers
included in their names, so the SONAME field is different.  Whitelist
the 'lite' and 'full' versions to have different core and vendor
variants.

Test: Build a device with TARGET_VNDK_USE_CORE_VARIANT set.
Change-Id: I9880a5d7172a9f35f304af8e7dcababdcbc2ca23

cc/config/vndk.go

@@ -120,6 +120,8 @@ var VndkMustUseVendorVariantList = []string{
 	"libmedia_omx",
 	"libmemtrack",
 	"libnetutils",
+	"libprotobuf-cpp-full",
+	"libprotobuf-cpp-lite",
 	"libpuresoftkeymasterdevice",
 	"libradio_metadata",
 	"libselinux",