patch 9.0.1577: MS-Windows: context menu translations may be wrong

Problem:    MS-Windows: context menu translations may be wrong.
Solution:   Set the encoding before using gettext(). (Ken Takata,
            closes #12441, closes #12431)
diff --git a/src/GvimExt/Make_ming.mak b/src/GvimExt/Make_ming.mak
index 0ebe08a..85017d8 100644
--- a/src/GvimExt/Make_ming.mak
+++ b/src/GvimExt/Make_ming.mak
@@ -43,9 +43,9 @@
 DEL = del
 endif
 endif
-# Set the default $(WINVER) to make it work with WinXP.
+# Set the default $(WINVER) to make it work with Windows 7.
 ifndef WINVER
-WINVER = 0x0501
+WINVER = 0x0601
 endif
 CXX := $(CROSS_COMPILE)g++
 WINDRES := $(CROSS_COMPILE)windres