Fix symbol.py's toolchain detection for x86.

x86 uses the x86_64 toolchain. There's no separate 32-bit toolchain.

I started to refactor so we could add FindToolchain tests, but that doesn't
work because FindToolchain depends on environment variables set up by 'lunch'.

Change-Id: I264b95e1e83a7e795f8cac49bc9e1cf497514029
3 files changed