Update scripts for per-board libraries.

Update the various scripts for compiler libraries being built on a
per-board bases, rather than on a per-architecture bases.

BUG=chromium:197654
TEST=Successfully built and installed the compiler and the libraries
(libstdc++, libgcc) separately, using their (new) separate ebuild.
Successfully built and tested (with the three CLs) on remote trybots for
x86-alex-full, lumpy-full and daisy-full.

CQ-DEPEND=CL:60289
CQ-DEPEND=CL:60350

Change-Id: I557c826e5a22500e225ccd3b71555b1fb98ac3ed
Reviewed-on: https://chromium-review.googlesource.com/60303
Reviewed-by: Caroline Tice <cmtice@chromium.org>
Tested-by: Caroline Tice <cmtice@chromium.org>
Commit-Queue: Caroline Tice <cmtice@chromium.org>
4 files changed