We prepended Soong's binary installation path to PATH, but now
rebuilding binaries that are in Soong and exported to Make produces
inconsistent results. From an empty out directory:
Run `m -j hidl-gen`, PATH will get a hidl-gen binary in out/host/...
Run `m -j android.hardware.tests.foo@1.0`, PATH will get a new hidl-gen
binary in out/soong/host/...
Make a change to hidl-gen, then run `m -j hidl-gen`. The hidl-gen first
in PATH is still the one without the changes.
Bug: 31742855
Test: m -j hidl-gen showcommands
Change-Id: If01a76d10d786dac6f16f31d1142634af4964228