Windows Support: Fixup Perl build (#29711)

* Add pl2bat to PATH: Windows on Perl requires the script pl2bat.bat
  and Perl to be available to the installer via the PATH. The build
  and dependent environments of Perl on Windows have the install
  prefix bin added to the PATH.
* symlink with win32file module instead of using Executable to
  call mklink (mklink is a shell function and so is not accessible
  in this manner).

lib/spack/llnl/util/symlink.py

@@ -11,10 +11,11 @@
 
 from llnl.util import lang
 
-from spack.util.executable import Executable
-
 is_windows = _platform == 'win32'
 
+if is_windows:
+    from win32file import CreateHardLink
+
 
 def symlink(real_path, link_path):
     """
@@ -53,16 +54,7 @@ def _win32_junction(path, link):
         path = os.path.join(parent, path)
         path = os.path.abspath(path)
 
-    command = "mklink"
+    CreateHardLink(link, path)
-    default_args = [link, path]
-    if os.path.isdir(path):
-        # try using a junction
-        default_args.insert(0, '/J')
-    else:
-        # try using a hard link
-        default_args.insert(0, '/H')
-
-    Executable(command)(*default_args)
 
 
 @lang.memoized

var/spack/repos/builtin/packages/perl/package.py

@@ -15,6 +15,7 @@
 import os
 import platform
 import re
+import sys
 from contextlib import contextmanager
 
 from llnl.util.lang import match_predicate
@@ -23,7 +24,7 @@
 from spack import *
 from spack.operating_systems.mac_os import macos_version
 
-is_windows = str(spack.platforms.host()) == 'windows'
+is_windows = sys.platform == 'win32'
 
 
 class Perl(Package):  # Perl doesn't use Autotools, it should subclass Package
@@ -330,6 +331,8 @@ def _setup_dependent_env(self, env, dependent_spec, deptypes):
         if perl_lib_dirs:
             perl_lib_path = ':'.join(perl_lib_dirs)
             env.prepend_path('PERL5LIB', perl_lib_path)
+        if is_windows:
+            env.append_path('PATH', self.prefix.bin)
 
     def setup_dependent_build_environment(self, env, dependent_spec):
         self._setup_dependent_env(env, dependent_spec,
@@ -361,6 +364,7 @@ def setup_dependent_package(self, module, dependent_spec):
 
     def setup_build_environment(self, env):
         if is_windows:
+            env.append_path('PATH', self.prefix.bin)
             return
 
         spec = self.spec