eal/linux: fix build with glibc < 2.12

eal/linux: fix build with glibc < 2.12

pthread_setname_np() function added in glibc 2.12, using this function
in older glibc versions cause compile error:
error: implicit declaration of function "pthread_setname_np"

This patch adds "rte_thread_setname" macro and set it according
glibc >= 2.12 check, thread naming disabled for older glibc versions,
glibc versions that support "pthread_setname_np" will keep using this
function.

Fixes: 67b6d3039e9e ("eal: set name to threads")
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>