install_toolchain: put rpcsvc-proto in package.provided.

rpcvc-proto is a host package that are needed by target, we want
to put it into package.provided.

BUG=chromium:892195
TEST=run setup_board --board samus (package.provided not chanaged)
     run setup_board --board samus after emerging rpcvc-proto,
     net-libs/rpcvc-proto-1.3.1-r1 was shown in package.provided.

Change-Id: Ie748c0388a171ab2789da8d7a71a3ebb20c8c981
Reviewed-on: https://chromium-review.googlesource.com/1262084
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed