Arch Linux

Description:
In current python{,2}-protobuf package, `--cpp_implementation` is not enabled, which causes bad performance.
When I try load a 549MiB protobuf record, the current package in the repo takes about 8 minutes. However, after
repacking the package with `--cpp_implementation`, it takes only several seconds.

To run python{,2}-protobuf with `--cpp_implementation` compilation option requires protobuf package as its
depends, which is already satisfied in the current PKGUBILD.

Additional info:
* package version(s)
3.3.2-1

There are some discussions on performance here[1], and a building spec here[2]. And the attachment is a patch
for PKGBUILD.

How to reproduce:
In my case, the protobuf record can be found here[3], and the proto which defines the protocol can be found here[4].
They are really large things, so I list them here just for those who want to compare the performance.
To reproduce it,
1. compile the caffe.proto with `protoc --python_out=. caffe.proto`. This will produce a caffe_pb2.py
2. run `python -c 'import caffe_pb2; net = caffe_pb2.NetParameter(); net.ParseFromString(open("VGG_ILSVRC_19_layers.caffemodel", "rb").read())'`.

[1] https://github.com/google/protobuf/issues/880
[2] https://github.com/google/protobuf/blob/master/python/README.md
[3] http://www.robots.ox.ac.uk/~vgg/software/very_deep/caffe/VGG_ILSVRC_19_layers.caffemodel
[4] https://github.com/BVLC/caffe/blob/master/src/caffe/proto/caffe.proto