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/Makefile b/src/Makefile
index 38bb109..7e2a843 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1626,6 +1626,7 @@
 	screen.c \
 	search.c \
 	sha256.c \
+	sign.c \
 	spell.c \
 	spellfile.c \
 	syntax.c \
@@ -1736,6 +1737,7 @@
 	objects/screen.o \
 	objects/search.o \
 	objects/sha256.o \
+	objects/sign.o \
 	objects/spell.o \
 	objects/spellfile.o \
 	objects/syntax.o \
@@ -1870,6 +1872,7 @@
 	screen.pro \
 	search.pro \
 	sha256.pro \
+	sign.pro \
 	spell.pro \
 	spellfile.pro \
 	syntax.pro \
@@ -3200,6 +3203,9 @@
 objects/sha256.o: sha256.c
 	$(CCC) -o $@ sha256.c
 
+objects/sign.o: sign.c
+	$(CCC) -o $@ sign.c
+
 objects/spell.o: spell.c
 	$(CCC) -o $@ spell.c
 
@@ -3586,6 +3592,10 @@
  auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
  proto.h globals.h farsi.h arabic.h
+objects/sign.o: sign.c vim.h protodef.h auto/config.h feature.h os_unix.h \
+ auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
+ proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
+ proto.h globals.h farsi.h arabic.h
 objects/spell.o: spell.c vim.h protodef.h auto/config.h feature.h os_unix.h \
  auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \