cros_setup_toolchains: Install llvm-libunwind before libc++

Make sure that llvm-libunwind is already installed
before building libc++.

BUG=b:187794119
TEST=sdk tryjob

Change-Id: Ie605f42e39d043700047effddec4ae146643b223
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3079463
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Christopher Di Bella <cjdb@google.com>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Christopher Di Bella <cjdb@google.com>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 520e76a..14825c1 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -105,9 +105,9 @@
 )
 
 LLVM_PKGS_TABLE = {
+    'ex_llvm-libunwind' : ['--ex-pkg', 'sys-libs/llvm-libunwind'],
     'ex_libcxxabi' : ['--ex-pkg', 'sys-libs/libcxxabi'],
     'ex_libcxx' : ['--ex-pkg', 'sys-libs/libcxx'],
-    'ex_llvm-libunwind' : ['--ex-pkg', 'sys-libs/llvm-libunwind'],
 }
 
 class Crossdev(object):
@@ -120,10 +120,10 @@
   MANUAL_PKGS = {
       'rust': 'dev-lang',
       'llvm': 'sys-devel',
+      'llvm-libunwind': 'sys-libs',
       'libcxxabi': 'sys-libs',
       'libcxx': 'sys-libs',
       'elfutils': 'dev-libs',
-      'llvm-libunwind': 'sys-libs',
   }
 
   @classmethod