Fix build issues on mips by using the same v8_torque_toolchain (renamed
to v8_generator_toolchain), which is the same as the host tool chain
when targeting MIPS.

Bug: v8:8162
Change-Id: I5d213398cba4c5e108b203e6aa6ba5a2b0e8f781
Reviewed-on: https://chromium-review.googlesource.com/1221289
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55844}