toolchain_build: Avoid embedding absolute paths in gcc binary
toolchain_build: Avoid embedding absolute paths in gcc binary

Currently, the working directory name on the bot leaks into the
gcc binary.  As well as exposing something users should not
really see, this means a repeated build might have a different
output hash just because it ran on a slightly different bot.
We want to avoid that.

BUG= none
TEST= toolchain trybots
R=bradnelson@google.com

Review URL: https://codereview.chromium.org/18286003

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@11710 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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