mk: fix missing librt dependencies

For GLIBC < 2.17 it is necessery to add -lrt for linker
from glibc > 2.17 The `clock_*' suite of functions (declared in <time.h>) is now
available directly in the main C library. This affect Ubuntu 12.04 in i686
and other older Linux Distros).

Fixes: 4758404a30 ("mk: fix eal shared library dependencies")

Signed-off-by: Daniel Mrzyglod <danielx.t.mrzyglod@intel.com>

app/test/Makefile

@@ -114,6 +114,7 @@ SRCS-$(CONFIG_RTE_LIBRTE_CMDLINE) += test_cmdline_string.c
 SRCS-$(CONFIG_RTE_LIBRTE_CMDLINE) += test_cmdline_lib.c
 
 ifeq ($(CONFIG_RTE_LIBRTE_SCHED),y)
+LDLIBS += -lrt
 SRCS-y += test_red.c
 SRCS-y += test_sched.c
 endif

examples/ptpclient/Makefile

@@ -46,6 +46,7 @@ SRCS-y := ptpclient.c
 
 CFLAGS += -O3
 CFLAGS += $(WERROR_FLAGS)
+LDLIBS += -lrt
 
 # workaround for a gcc bug with noreturn attribute
 # http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12603

lib/librte_eal/linuxapp/eal/Makefile

@@ -52,6 +52,7 @@ CFLAGS += $(WERROR_FLAGS) -O3
 LDLIBS += -ldl
 LDLIBS += -lpthread
 LDLIBS += -lgcc_s
+LDLIBS += -lrt
 
 # specific to linuxapp exec-env
 SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) := eal.c