rtc.c test: fix for clang
rtc.c test: fix for clang

clang complains:
> clang -g -O2 -Wall -Werror -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=0  -iquote ../lib/arch/x86/include -I../lib   rtc.c ../lib/libzdtmtst.a ../lib/libzdtmtst.a -o rtc
> rtc.c:50:7: error: taking the absolute value of unsigned type 'unsigned long' has no effect [-Werror,-Wabsolute-value]
>                 if (labs(delta - 1000000 / TEST_HZ ) > 100000) {
>                     ^

Declare delta as long.

Signed-off-by: Kir Kolyshkin <c0159612b0ef32139322233232df1a0d189c4b9b@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu