Use the Soong output as the checkbuild target

Save disk space when building checkbuild by avoiding copying the Soong
output file into the Make intermediates directory.

All the same files in out/soong that were created by m checkbuild before
this patch are still created after this patch.  In the internal branch
the total size of the out directory after m checkbuild is reduced from
1320 GB to 965 GB.

Bug: 201816050
Test: m checkbuild
Change-Id: I6370df44f9baab00fcfe30c072600fe58109954d