Patrick Doyle writes:

target/device/Soekris/net4521/linux.mk is missing an endif for 
the first if statement

target/device/Soekris/Makefile.in needs to set TARGETS before 
including linux.mk since the file checks the TARGETS variables

target/device/Soekris/Makefile.in

@@ -4,9 +4,8 @@ UCLIBC_CONFIG_FILE:=target/device/Soekris/net4521/uClibc.config
 BR2_PACKAGE_BUSYBOX_CONFIG:=target/device/Soekris/net4521/busybox.config
 
 ifeq ($(strip $(BR2_PACKAGE_LINUX)),y)
-include target/device/Soekris/net4521/linux.mk
 TARGETS+=linux
+include target/device/Soekris/net4521/linux.mk
 endif
 
 endif
-

target/device/Soekris/net4521/linux.mk

@@ -122,3 +122,4 @@ linuxclean: clean
 linux-dirclean:
 	rm -rf $(LINUX_DIR)
 
+endif