Fix the order of library linking for cpc samples

Fixes the following compilation failure

$ make testcpc

cc   barrier.o  -L../runtime -lm -pthread -lcpcfull -o barrier
../runtime/libcpcfull.a(cpc_libev.o): In function `periodic_recalc':
/home/prasad/KVM/cpc/runtime/libev/ev.c:2218: undefined reference to `ceil'
/home/prasad/KVM/cpc/runtime/libev/ev.c:2218: undefined reference to `ceil'
/home/prasad/KVM/cpc/runtime/libev/ev.c:2218: undefined reference to `ceil'
collect2: ld returned 1 exit status
make[1]: *** [barrier] Error 1
rm barrier.cpi barrier.c
make[1]: Leaving directory `/home/prasad/KVM/cpc/samples'
make: *** [testcpc] Error 2

Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>