Added the MAKE_VERSION global that could be useful in determining

if a given make(1) is feature-compatible with a set of makefiles.

When merged, this will be used to replace the ugly upgrade_checks
hacks in src/Makefile.

Version has the RYYYYMMDDX format, where R is from RELENG_<R> and
X allows for 10 distinguishable changes per day.

Discussed with:	bde

usr.bin/make/Makefile

@@ -15,6 +15,10 @@ SRCS+=	lstAppend.c lstAtEnd.c lstAtFront.c lstClose.c lstConcat.c \
 
 NOSHARED?=	YES
 
+CFLAGS+=-DMAKE_VERSION=\"5200205220\"
+
+main.o: ${MAKEFILE}
+
 # Set the shell which make(1) uses.  Bourne is the default, but a decent
 # Korn shell works fine, and much faster.  Using the C shell for this
 # will almost certainly break everything, but it's Unix tradition to

usr.bin/make/main.c

@@ -659,6 +659,9 @@ main(argc, argv)
 	Var_Set("MACHINE", machine, VAR_GLOBAL);
 	Var_Set("MACHINE_ARCH", machine_arch, VAR_GLOBAL);
 	Var_Set("MACHINE_CPU", machine_cpu, VAR_GLOBAL);
+#ifdef MAKE_VERSION
+	Var_Set("MAKE_VERSION", MAKE_VERSION, VAR_GLOBAL);
+#endif
 
 	/*
 	 * First snag any flags out of the MAKE environment variable.