common: Fix stringstream include in platform.h

Change-Id: I56daf62f70de3228d695f46750419dcc268d8e99
external: Import crcutil sources

Until now crcutil was downloaded when needed during build. This had some
downsides, like that the sources could not be compiled without access to
the web. This commit changes that.

Change-Id: I6e6074a7f7ce1196c53a136a14c9ee2be86f5d53