test: minor updates to improve virtiofs pass rate

[benhillis]

Resolve a few minor issues preventing some virtiofs tests from passing.

1. An incorrect error check when trying to map an app execution alias. This was causing the test to segfault and exit early. Was able to track this down because of test: improve test logging infra #13811.
2. Some test logic that needed to be updated to account for what virtiofs supports.

[Copilot]

Pull request overview

This PR resolves two distinct issues preventing virtiofs tests from passing reliably:

1. Fixed incorrect mmap error handling - Changed from LxtCheckNullErrno to LxtCheckMapErrno macro and properly initialized the mapping pointer with MAP_FAILED instead of NULL. This prevented segfaults when testing app execution aliases.
2. Updated test logic for virtiofs support - Added virtiofs-specific skip conditions to match existing plan9 behavior, and properly threaded the DrvFsMode parameter to enable conditional test logic.

• Updated DrvFsFat test to skip for VirtioFS (only supports full drive mounts)
• Added virtiofs checks alongside plan9 in multiple test skip conditions
• Fixed initialization order to set config before launching WSL
• Updated comments to reflect virtiofs limitations

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/windows/DrvFsTests.cpp	Added DrvFsMode parameter to DrvFsFat, added VirtioFS skip logic, fixed test setup initialization order to apply config before launching WSL
test/linux/unit_tests/drvfs.c	Fixed mmap error checking (LxtCheckMapErrno + MAP_FAILED), added virtiofs skip conditions matching plan9 behavior, updated comments

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.