procutil: add a shim for translating shell commands to native commands

mercurial/hook.py

@@ -139,9 +139,7 b' def _exthook(ui, repo, htype, name, cmd,'
             v = stringutil.pprint(v)
         env['HG_' + k.upper()] = v
 
-    if pycompat.iswindows:
-        environ = procutil.shellenviron(env)
-        cmd = util.platform.shelltocmdexe(cmd, environ)
+    cmd = procutil.shelltonative(cmd, env)
 
     ui.note(_("running hook %s: %s\n") % (name, cmd))
 

mercurial/utils/procutil.py

@@ -317,6 +317,13 b' def shellenviron(environ=None):'
     env['HG'] = hgexecutable()
     return env
 
+if pycompat.iswindows:
+    def shelltonative(cmd, env):
+        return platform.shelltocmdexe(cmd, shellenviron(env))
+else:
+    def shelltonative(cmd, env):
+        return cmd
+
 def system(cmd, environ=None, cwd=None, out=None):
     '''enhanced shell command execution.
     run with environment maybe modified, maybe in different dir.