Delay actually opening log files until the first write, fix #1724

Calling DepsLog/BuildLog::OpenForWrite will now only save the file path.
The actual opening of the file (moved to OpenForWriteIfNeeded) happens
right before the first write attempt.

This is needed so that the files aren't held open when the generator
runs (i.e. RebuildManifest) as it may call tools like recompact which
won't be able to open the file on Windows.

The disadvantage is that now the error reporting happens at a later time
and will be reported as a failed write, not a failed open.

0 files changed, 0 insertions, 0 deletions