Tests/BuildDepends: Drop unneeded help for Ninja

The extra post-modification invocations of 'ninja' does not seem to be
needed anymore for the BuildDepends test to pass.
Ninja: Use a TARGET_FILE variable to hold the link output file

Use an explicit "$TARGET_FILE" variable instead of "$out" so that
we can have multiple output files while still only referencing the
main one in command lines.
Ninja: Refactor restat to be a string internally

This will allow values other than "" and "1" to be generated in
the rules.ninja file.
Merge topic 'ninja-minor-refactoring'

67bd514a Ninja: Refactor restat to be a string internally
ef42e57d Ninja: Use a TARGET_FILE variable to hold the link output file
592644c4 Tests/BuildDepends: Drop unneeded help for Ninja