patch 8.1.1210: support for user commands is spread out

Problem:    Support for user commands is spread out. No good reason to make
            user commands optional.
Solution:   Move user command support to usercmd.c.  Always enable the
            user_commands feature.
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 3c01e63..599b9ee 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -757,6 +757,7 @@
 	$(OUTDIR)/textprop.o \
 	$(OUTDIR)/ui.o \
 	$(OUTDIR)/undo.o \
+	$(OUTDIR)/usercmd.o \
 	$(OUTDIR)/userfunc.o \
 	$(OUTDIR)/version.o \
 	$(OUTDIR)/vimrc.o \