[Bug other/78196] New: GCC self-test breaks native Windows builds

[tamar.christina at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78196

            Bug ID: 78196
           Summary: GCC self-test breaks native Windows builds
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tamar.christina at arm dot com
  Target Milestone: ---

The GCC self-test added in r237144 breaks the native Windows builds (e.g.
mingw-w64).

The test essentially does `-xc -S -c /dev/null -fself-test`

`/dev/null` is then converted into the Windows null device `nul` by the MSYS
shell, which is correct. But then the driver adds a filename to the name,
trying to write the output to `nul.s`. `nul` is a reserved filename on Windows.
As such it's invalid to create this file and the call always fails using
CreateFile.

This makes you unable to make native windows builds of GCC 7.