patch 8.1.0483: MinGW does not build tee.exe

Problem:    MinGW does not build tee.exe.
Solution:   Add build instructions. (Yasuhiro Matsumoto, closes #3548)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index f5f134b..f30fe2f 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -943,7 +943,7 @@
 LFLAGS += -Wl,-Map=$(TARGET).map
 endif
 
-all: $(TARGET) vimrun.exe xxd/xxd.exe install.exe uninstal.exe GvimExt/gvimext.dll
+all: $(TARGET) vimrun.exe xxd/xxd.exe tee/tee.exe install.exe uninstal.exe GvimExt/gvimext.dll
 
 vimrun.exe: vimrun.c
 	$(CC) $(CFLAGS) -o vimrun.exe vimrun.c $(LIB)
@@ -968,6 +968,9 @@
 xxd/xxd.exe: xxd/xxd.c
 	$(MAKE) -C xxd -f Make_ming.mak CC='$(CC)'
 
+tee/tee.exe: tee/tee.c
+	$(MAKE) -C tee CC='$(CC)'
+
 GvimExt/gvimext.dll: GvimExt/gvimext.cpp GvimExt/gvimext.rc GvimExt/gvimext.h
 	$(MAKE) -C GvimExt -f Make_ming.mak CROSS=$(CROSS) CROSS_COMPILE=$(CROSS_COMPILE) CXX='$(CXX)' STATIC_STDCPLUS=$(STATIC_STDCPLUS)
 
@@ -996,6 +999,7 @@
 endif
 	$(MAKE) -C GvimExt -f Make_ming.mak clean
 	$(MAKE) -C xxd -f Make_ming.mak clean
+	$(MAKE) -C tee clean
 
 ###########################################################################
 INCL =	vim.h alloc.h arabic.h ascii.h ex_cmds.h farsi.h feature.h globals.h \