patch 8.1.1933: the eval.c file is too big

Problem:    The eval.c file is too big.
Solution:   Move code related to variables to evalvars.c. (Yegappan
            Lakshmanan, closes #4868)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index bb4c739..e362815 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -722,6 +722,7 @@
 	$(OUTDIR)/edit.o \
 	$(OUTDIR)/eval.o \
 	$(OUTDIR)/evalfunc.o \
+	$(OUTDIR)/evalvars.o \
 	$(OUTDIR)/ex_cmds.o \
 	$(OUTDIR)/ex_cmds2.o \
 	$(OUTDIR)/ex_docmd.o \