Fix "Nothing to be done" messages when launching soong_ui

When specifying multiple arguments to make, we were getting messages
about nothing to be done:

m -j USE_SOONG_UI=true checkbuild tests cts blueprint_tools
...
make: Nothing to be done for `tests'.
make: Nothing to be done for `cts'.
make: Nothing to be done for `blueprint_tools'.

Test: m -j USE_SOONG_UI=true blueprint_tools libc adb
Change-Id: Id448bf0e09736fcd92ba058aec7ce556f6f778a3