patch 8.1.2045: the option.c file is too big

Problem:    The option.c file is too big.
Solution:   Split off the code dealing with strings. (Yegappan Lakshmanan,
            closes #4937)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index f9c5367..9d8abf8 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -757,6 +757,7 @@
 	$(OUTDIR)/normal.o \
 	$(OUTDIR)/ops.o \
 	$(OUTDIR)/option.o \
+	$(OUTDIR)/optionstr.o \
 	$(OUTDIR)/os_mswin.o \
 	$(OUTDIR)/os_win32.o \
 	$(OUTDIR)/pathdef.o \