cmake: fix lookup of external libraries

In order to make it compile properly in more environments.

Tested-by: Petr Novák <petrn@me.com>
Tested-by: Kuan-Yi Li <kyli@abysm.org>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

CMakeLists.txt

@@ -25,7 +25,13 @@ IF(NOT DISABLE_INIT)
   SET(SOURCES ${SOURCES} watchdog.c plug/coldplug.c plug/hotplug.c)
 ENDIF()
 
-SET(LIBS ubox ubus json-c blobmsg_json json_script)
+FIND_LIBRARY(ubox NAMES ubox)
+FIND_LIBRARY(ubus NAMES ubus)
+FIND_LIBRARY(blobmsg_json NAMES blobmsg_json)
+FIND_LIBRARY(json_script NAMES json_script)
+FIND_LIBRARY(json NAMES json-c json)
+
+SET(LIBS ${ubox} ${ubus} ${json} ${blobmsg_json} ${json_script})
 
 IF(DEBUG)
   ADD_DEFINITIONS(-DUDEV_DEBUG -g3)
@@ -90,7 +96,7 @@ ADD_CUSTOM_TARGET(capabilities-names-h DEPENDS capabilities-names.h)
 IF(SECCOMP_SUPPORT)
 ADD_DEFINITIONS(-DSECCOMP_SUPPORT)
 ADD_LIBRARY(preload-seccomp SHARED jail/preload.c jail/seccomp.c)
-TARGET_LINK_LIBRARIES(preload-seccomp dl ubox blobmsg_json)
+TARGET_LINK_LIBRARIES(preload-seccomp dl ${ubox} ${blobmsg_json})
 INSTALL(TARGETS preload-seccomp
 	LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
 )
@@ -99,7 +105,7 @@ endif()
 
 IF(JAIL_SUPPORT)
 ADD_EXECUTABLE(ujail jail/jail.c jail/elf.c jail/fs.c jail/capabilities.c)
-TARGET_LINK_LIBRARIES(ujail ubox blobmsg_json)
+TARGET_LINK_LIBRARIES(ujail ${ubox} ${blobmsg_json})
 INSTALL(TARGETS ujail
 	RUNTIME DESTINATION ${CMAKE_INSTALL_SBINDIR}
 )
@@ -108,7 +114,7 @@ endif()
 
 IF(UTRACE_SUPPORT)
 ADD_EXECUTABLE(utrace trace/trace.c)
-TARGET_LINK_LIBRARIES(utrace ubox ${json} blobmsg_json)
+TARGET_LINK_LIBRARIES(utrace ${ubox} ${json} ${blobmsg_json})
 INSTALL(TARGETS utrace
 	RUNTIME DESTINATION ${CMAKE_INSTALL_SBINDIR}
 )

upgraded/CMakeLists.txt

@@ -5,7 +5,7 @@ FIND_PATH(ubox_include_dir libubox/uloop.h)
 INCLUDE_DIRECTORIES(${ubox_include_dir})
 ADD_DEFINITIONS(-Os -ggdb -Wall -Werror --std=gnu99 -Wmissing-declarations)
 ADD_EXECUTABLE(upgraded upgraded.c ../watchdog.c)
-TARGET_LINK_LIBRARIES(upgraded ubox)
+TARGET_LINK_LIBRARIES(upgraded ${ubox})
 INSTALL(TARGETS upgraded
 	RUNTIME DESTINATION sbin
 )