Otherwise Make and soong_ui disagree about where the soong.variables
file should be. For example, when "OUT_DIR=out/":
Error dumping make vars: Failed to parse make line: "make: Nothing to be done for `out/soong/soong.variables'."
We would need to pass out//soong/soong.variables into make, since it
doesn't attempt to match clean/unclean paths.
Bug: 37553659
Test: OUT_DIR=out/ m -j
Change-Id: Iebeea4868b96b11e8b08735f272e22be5db1d701