dhcpcd: needs MMU

dhcpcd fails to build on non-MMU platforms, even with the
--disable-fork option:

  bind.o: In function `_daemonise':
  bind.c:(.text+0x62): undefined reference to `_fork'
  collect2: ld returned 1 exit status

Therefore, we make dhcpcd depend on MMU support, and remove the
non-MMU condition in the .mk file. More recent versions of dhcpcd do
support non-MMU properly, but this commit intends to be only a fix.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Samuel Martin <s.martin49@gmail.com>

package/dhcpcd/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_DHCPCD
 	depends on BR2_INET_IPV6
+	depends on BR2_USE_MMU # fork()
 	bool "dhcpcd"
 	help
 	  An RFC2131 compliant DHCP client

package/dhcpcd/dhcpcd.mk

@@ -9,10 +9,6 @@ DHCPCD_SOURCE = dhcpcd-$(DHCPCD_VERSION).tar.bz2
 DHCPCD_SITE = http://roy.marples.name/downloads/dhcpcd/
 DHCPCD_LICENSE = BSD-2c
 
-ifeq ($(BR2_USE_MMU),)
-	DHCPCD_CONFIG_OPT += --disable-fork
-endif
-
 define DHCPCD_CONFIGURE_CMDS
 	(cd $(@D); \
 	./configure \