Don't compile programs using fork() on MMU-less systems

Systems that lack a MMU cannot use fork() to create the child process.
The patch does not compile the affected programs on MMU-less systems.

Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

Makefile

@@ -45,6 +45,8 @@ MAKEFLAGS := -k
 
 CFLAGS := -O2 -Wall -Wno-parentheses
 
+HAVE_FORK := $(shell ./check_cc.sh "$(CC)" fork_test.c)
+
 CPPFLAGS += \
 	-I. \
 	-Iinclude \
@@ -66,10 +68,14 @@ PROGRAMS_ISOTP := \
 	isotpperf \
 	isotprecv \
 	isotpsend \
-	isotpserver \
 	isotpsniffer \
 	isotptun
 
+ifeq ($(HAVE_FORK),1)
+PROGRAMS_ISOTP += \
+	isotpserver
+endif
+
 PROGRAMS_J1939 := \
 	j1939acd \
 	j1939cat \
@@ -87,14 +93,12 @@ PROGRAMS := \
 	$(PROGRAMS_J1939) \
 	$(PROGRAMS_SLCAN) \
 	asc2log \
-	bcmserver \
 	can-calc-bit-timing \
 	canbusload \
 	candump \
 	canfdtest \
 	cangen \
 	cansequence \
-	canlogserver \
 	canplayer \
 	cansend \
 	cansniffer \
@@ -103,6 +107,12 @@ PROGRAMS := \
 	mcp251xfd-dump \
 	slcanpty
 
+ifeq ($(HAVE_FORK),1)
+PROGRAMS += \
+	canlogserver \
+	bcmserver
+endif
+
 all: $(PROGRAMS)
 
 clean: