buld_error protobuf file is created the moment a build action failed.
This is for external system to detect immediately what caused the
build failure while monitoring the build_progress.pb file.
Bug: b/150401146
Test: * m nothing
* Built successfully aosp_arm-eng and checked build_error file
was not created.
* Modified a cpp file to cause a build failed. Ran m and build
failed. Checked immediately during the build that the
build_error file was created.
* m clean; m and during build, checked if build_error was
removed.
Change-Id: I778616ae8cf242b49ad263b79c93321959112caa
85f227eed7