patch 8.1.0474: directory where if_perl.c is written is inconsistent

Problem:    Directory where if_perl.c is written is inconsistent.
Solution:   use auto/if_perl.c for MS-Windows. (Ken Takata, closes #3540)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index f381951..65a1fbf 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -985,6 +985,7 @@
 	-$(DEL) pathdef.c
 ifdef PERL
 	-$(DEL) if_perl.c
+	-$(DEL) auto$(DIRSLASH)if_perl.c
 endif
 ifdef MZSCHEME
 	-$(DEL) mzscheme_base.c
@@ -1043,10 +1044,14 @@
 $(OUTDIR)/if_ole.o:	if_ole.cpp $(INCL) if_ole.h
 	$(CC) $(CFLAGS) $(CXXFLAGS) -c -o $(OUTDIR)/if_ole.o if_ole.cpp
 
-if_perl.c:		if_perl.xs typemap
+auto/if_perl.c:		if_perl.xs typemap
 	$(XSUBPP) -prototypes -typemap \
 	     $(PERLTYPEMAP) if_perl.xs -output $@
 
+$(OUTDIR)/if_perl.o:	auto/if_perl.c $(INCL)
+	$(CC) -c $(CFLAGS) auto/if_perl.c -o $(OUTDIR)/if_perl.o
+
+
 $(OUTDIR)/if_ruby.o:	if_ruby.c $(INCL)
 ifeq (16, $(RUBY))
 	$(CC) $(CFLAGS) -U_WIN32 -c -o $(OUTDIR)/if_ruby.o if_ruby.c