patch 8.1.0673: functionality for signs is spread out over several files

Problem:    Functionality for signs is spread out over several files.
Solution:   Move most of the sign functionality into sign.c. (Yegappan
            Lakshmanan, closes #3751)
diff --git a/src/Make_dice.mak b/src/Make_dice.mak
index c53f182..2daa8d7 100644
--- a/src/Make_dice.mak
+++ b/src/Make_dice.mak
@@ -71,6 +71,7 @@
 	screen.c \
 	search.c \
 	sha256.c \
+	sign.c \
 	spell.c \
 	spellfile.c \
 	syntax.c \
@@ -127,6 +128,7 @@
 	o/screen.o \
 	o/search.o \
 	o/sha256.o \
+	o/sign.o \
 	o/spell.o \
 	o/spellfile.o \
 	o/syntax.o \
@@ -252,6 +254,8 @@
 
 o/sha256.o:	sha256.c  $(SYMS)
 
+o/sign.o:	sign.c  $(SYMS)
+
 o/spell.o:	spell.c  $(SYMS) spell.h
 
 o/spellfile.o:	spellfile.c  $(SYMS) spell.h