При линковке статической библиотеки не подключается glibc

include_directories(${GTK_INCLUDE_DIRS}
                    ${PROJECT_SOURCE_DIR}/include/lxpanelx
                    ${PROJECT_SOURCE_DIR}
                    ${PROJECT_SOURCE_DIR}/src  
                    )
set(PLUGINS_SOURCES launchbutton.c
                    dclock.c
                    separator.c
                    pager.c
                    space.c
                    tray.c
                    wincmd.c
                    dirmenu.c
                    ${MENU_SOURCES})
add_library(builtin_plugins STATIC ${PLUGINS_SOURCES})

plugins/libbuiltin_plugins.a(launchbutton.c.o): In function `input_start':
launchbutton.c:(.text+0x694): undefined reference to `openpty'