patch 9.0.2089: sound_playfile() fails when using powershell

Problem:  sound_playfile() fails when using powershell
Solution: quote filename using doublequotes, don't escape filename,
          because it doesn't use the shell

Avoiding powershell escaping because mci open command doesn't support
single quoted filenames: open 'C:\whatever\sound.wav' is not valid.

closes: #13471

Signed-off-by: GuyBrush <miguel.barro@live.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 5573a58..bc2516c 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1272,7 +1272,7 @@
 $(VIM): $(VIM).exe
 
 $(OUTDIR):
-	if not exist $(OUTDIR)/nul  mkdir $(OUTDIR)
+	if not exist $(OUTDIR)/nul  mkdir $(OUTDIR:/=\)
 
 CFLAGS_INST = /nologo /O2 -DNDEBUG -DWIN32 -DWINVER=$(WINVER) -D_WIN32_WINNT=$(WINVER) $(CFLAGS_DEPR)