[test spec] Write runtime deps to a canonical location.

host_tests.json may be used to find test specs printed to the root out
dir of //build/toolchain:host_${host_cpu}. Have write_runtime_deps write
to the same root out dir, so that these files may be discovered
alongside each other.

Change-Id: Ib460cd5a4aaf2018e0de61dd7b071fa7b2f21a21
1 file changed