Fix scons error message that occur early on.
Fix scons error message that occur early on.

Previously error message that occured early in scons
startup would cause exceptions in the atexit() handler.

TEST= ./scons --nacl_glibc=foobar
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/106743006

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@12500 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client