[phobos] std.datetime unittests fail on linux

[Walter Bright]

ok, that works

Brad Roberts wrote:
> Add -L-lrt to the DFLAGS variable in dmd.conf
>
> On 12/15/2010 12:03 AM, Walter Bright wrote:
>   
>> generated/linux/debug/unittest/std/datetime.o: In function `_D3std8datetime5Tick
>> s12_staticCtor1OFNeZv':
>> /home/walter/cbx/mars/phobos/std/datetime.d:80: undefined reference to `clock_ge
>> tres'
>> generated/linux/debug/unittest/std/datetime.o: In function `_D3std8datetime7syst
>> imeFNeZS3std8datetime5Ticks':
>> /home/--- errorlevel 1
>> make[1]: Leaving directory `/home/walter/cbx/mars/phobos'
>> walter/cbx/mars/phobos/std/datetime.d:666: undefined reference to `clock_gettime
>> '
>> collect2: ld returned 1 exit status
>> make[2]: *** [generated/linux/debug/unittest/std/datetime] Error 1
>> make[1]: *** [unittest] Error 2
>> make: *** [unittest] Error 2
>>
>>