cros_setup_toolchains: Add llvm-libunwind to host pkgs.

llvm-libunwind is part of toolchain and should have been in the
host pkg list.

BUG=chromium:944939
TEST=chromiumos-sdk passes.

Change-Id: Id659ab62635f97d9a2a4dce0693b825c2faeff08
Reviewed-on: https://chromium-review.googlesource.com/1548658
Commit-Ready: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index ba5dda4..5f6fc61 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -61,6 +61,7 @@
     'sys-libs/glibc',
     'sys-libs/libcxx',
     'sys-libs/libcxxabi',
+    'sys-libs/llvm-libunwind',
 )
 
 # These packages are also installed into the host SDK.  However, they require