Windows path handling: change representation for paths with spaces (#42754)

Some builds on Windows break when encountering paths with spaces. This
reencodes some paths in Windows 8.3 filename format (when on Windows):
this serves as an equivalent identifier for the file, but in a form that
does not have spaces.

8.3 filenames are also truncated in length, which could be helpful, but
that is not the primary intended purpose of using this format.

Overall

* nmake/msbuild packages do this generally for the install prefix
* curl/perl require additional modifications (as written now, each package
  may require calls to `windows_sfn` to work when the Spack
  root/install/staging prefixes contain spaces)

Some items for follow-up:

* Spack itself does not create paths with spaces "on top" of whatever
  the user configures or where it is placed (e.g. the Spack root, the
  staging directory, etc.), so it might be possible to edit some of these
  paths once and avoid a proliferation of individual `windows_sfn`
  calls in individual packages.
* This approach may result in the insertion of 8.3-style paths into
  build artifacts (on Windows), handling this may require additional
  bookkeeping (e.g. when relocating).

lib/spack/llnl/util/filesystem.py

@@ -1240,6 +1240,47 @@ def get_single_file(directory):
     return fnames[0]
 
 
+@system_path_filter
+def windows_sfn(path: os.PathLike):
+    """Returns 8.3 Filename (SFN) representation of
+    path
+
+    8.3 Filenames (SFN or short filename) is a file
+    naming convention used prior to Win95 that Windows
+    still (and will continue to) support. This convention
+    caps filenames at 8 characters, and most importantly
+    does not allow for spaces in addition to other specifications.
+    The scheme is generally the same as a normal Windows
+    file scheme, but all spaces are removed and the filename
+    is capped at 6 characters. The remaining characters are
+    replaced with ~N where N is the number file in a directory
+    that a given file represents i.e. Program Files and Program Files (x86)
+    would be PROGRA~1 and PROGRA~2 respectively.
+    Further, all file/directory names are all caps (although modern Windows
+    is case insensitive in practice).
+    Conversion is accomplished by fileapi.h GetShortPathNameW
+
+    Returns paths in 8.3 Filename form
+
+    Note: this method is a no-op on Linux
+
+    Args:
+        path: Path to be transformed into SFN (8.3 filename) format
+    """
+    # This should not be run-able on linux/macos
+    if sys.platform != "win32":
+        return path
+    path = str(path)
+    import ctypes
+
+    k32 = ctypes.WinDLL("kernel32", use_last_error=True)
+    # stub Windows types TCHAR[LENGTH]
+    TCHAR_arr = ctypes.c_wchar * len(path)
+    ret_str = TCHAR_arr()
+    k32.GetShortPathNameW(path, ret_str, len(path))
+    return ret_str.value
+
+
 @contextmanager
 def temp_cwd():
     tmp_dir = tempfile.mkdtemp()