Don't link rt library in Mac OS X

[bluesalt]

librt (POSIX.1b Realtime Extensions library) is not available in Mac OS X, thus it should not be linked.

[bluesalt]

Actually I found that even the rt is disabled in Linux, the test still pass. Why the library is needed here ?

[yosukehara]

Thank you for your contribution and report.

It only happened errors to build LeoFS on Ubuntu-13.10 as the follows.
So we set "rt".

$ make
Scanning dependencies of target cutil
[ 10%] Building C object src/CMakeFiles/cutil.dir/lcu_cache.c.o
[ 20%] Building C object src/CMakeFiles/cutil.dir/lcu_hashmap.c.o
[ 30%] Building C object src/CMakeFiles/cutil.dir/lcu_slab.c.o
[ 40%] Building C object src/CMakeFiles/cutil.dir/lcu_lru.c.o
[ 50%] Building C object src/CMakeFiles/cutil.dir/lcu_string.c.o
Linking C static library libcutil.a
[ 50%] Built target cutil
Scanning dependencies of target test_suites
[ 60%] Building C object tests/CMakeFiles/test_suites.dir/main.c.o
[ 70%] Building C object tests/CMakeFiles/test_suites.dir/check_cache.c.o
[ 80%] Building C object tests/CMakeFiles/test_suites.dir/check_hashmap.c.o
[ 90%] Building C object tests/CMakeFiles/test_suites.dir/check_slab.c.o
[100%] Building C object tests/CMakeFiles/test_suites.dir/check_lru.c.o
Linking C executable test_suites
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libcheck.a(check_run.o): In function `srunner_run':
(.text+0x965): undefined reference to `timer_create'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libcheck.a(check_run.o): In function `srunner_run':
(.text+0x9b3): undefined reference to `timer_settime'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libcheck.a(check_run.o): In function `srunner_run':
(.text+0x9d9): undefined reference to `timer_delete'
collect2: error: ld returned 1 exit status
make[2]: *** [tests/test_suites] Error 1
make[1]: *** [tests/CMakeFiles/test_suites.dir/all] Error 2
make: *** [all] Error 2

[yosukehara]

I've merged your fix to the develop-branch.
d1af101...89ccec3

Thank you.