getdeps: Move print "Mapping scratch dir" to stderr

Summary:
Mapping scratch dir <from> -> <to> show up in the output of all the show dir commands on Windows, so removing it.
example: getdeps.py show-inst-dir eden

Reviewed By: wez

Differential Revision: D16092494

fbshipit-source-id: 910288a8d23c1d68c5e70b7b2dbb36ef53a326fc

build/fbcode_builder/getdeps/buildopts.py

@@ -14,6 +14,7 @@ import hashlib
 import ntpath
 import os
 import subprocess
+import sys
 import tempfile
 
 from .envfuncs import Env, add_path_entry, path_search
@@ -364,7 +365,9 @@ def setup_build_options(args, host_type=None):
 
         if is_windows():
             subst = create_subst_path(scratch_dir)
-            print("Mapping scratch dir %s -> %s" % (scratch_dir, subst))
+            print(
+                "Mapping scratch dir %s -> %s" % (scratch_dir, subst), file=sys.stderr
+            )
             scratch_dir = subst
 
     host_type = _check_host_type(args, host_type)