Enable build system guess tests on windows (#36971)

lib/spack/spack/cmd/create.py

@@ -715,7 +715,7 @@ def __call__(self, stage, url):
                 output = tar("--exclude=*/*/*", "-tf", stage.archive_file, output=str)
             except ProcessError:
                 output = ""
-        lines = output.split("\n")
+        lines = output.splitlines()
 
         # Determine the build system based on the files contained
         # in the archive.

lib/spack/spack/test/build_system_guess.py

@@ -3,8 +3,6 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
-import sys
-
 import pytest
 
 import spack.cmd.create
@@ -12,8 +10,6 @@
 import spack.util.executable
 import spack.util.url as url_util
 
-pytestmark = pytest.mark.skipif(sys.platform == "win32", reason="does not run on windows")
-
 
 @pytest.fixture(
     scope="function",