patch 8.2.1381: MS-Windows: crash with Python 3.5 when stdin is redirected

Problem:    MS-Windows: crash with Python 3.5 when stdin is redirected.
Solution:   Reconnect stdin. (Yasuhiro Matsumoto, Ken Takata, closes #6641)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 3b72001..d66ff71 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1026,6 +1026,9 @@
 ! ifndef PYTHON3_VER
 PYTHON3_VER = 36
 ! endif
+! ifndef DYNAMIC_PYTHON3_DLL
+DYNAMIC_PYTHON3_DLL = python$(PYTHON3_VER).dll
+! endif
 ! message Python3 requested (version $(PYTHON3_VER)) - root dir is "$(PYTHON3)"
 ! if "$(DYNAMIC_PYTHON3)" == "yes"
 !  message Python3 DLL will be loaded dynamically
@@ -1035,9 +1038,10 @@
 PYTHON3_INC = /I "$(PYTHON3)\Include" /I "$(PYTHON3)\PC"
 ! if "$(DYNAMIC_PYTHON3)" == "yes"
 CFLAGS = $(CFLAGS) -DDYNAMIC_PYTHON3 \
-		-DDYNAMIC_PYTHON3_DLL=\"python$(PYTHON3_VER).dll\"
+		-DDYNAMIC_PYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
 PYTHON3_LIB = /nodefaultlib:python$(PYTHON3_VER).lib
 ! else
+CFLAGS = $(CFLAGS) -DPYTHON3_DLL=\"$(DYNAMIC_PYTHON3_DLL)\"
 PYTHON3_LIB = $(PYTHON3)\libs\python$(PYTHON3_VER).lib
 ! endif
 !endif