Update build_tool.py to work for aosp-toolchain repos.

Fixed the build_tool.py so that it works for aosp binutils / gcc repos.

TEST=tested manually with a local binutils source tree and a local
binutils branch.
BUG=None

Change-Id: I4756abcf234651e18284be38e50d4b534aeff942
Reviewed-on: https://chrome-internal-review.googlesource.com/255905
Commit-Ready: Han Shen <shenhan@google.com>
Tested-by: Han Shen <shenhan@google.com>
Reviewed-by: Caroline Tice <cmtice@google.com>
2 files changed