[build] Check if std::atomic wait()/notify{_all}() is avaialble

Fixes builds on Debian stable, which currently fail with

ccache c++ -Ieval/io_latency.p -Ieval -I../eval -Iemper -I../emper -Iemper/io -I../emper/io -Iemper/include -I../emper/include -I/usr/include -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -Wextra -Wpedantic -Werror -std=c++2a -O2 -g -DBOOST_ALL_NO_LIB -pthread -isystem../subprojects/liburing-liburing-2.0/src/include -isystemsubprojects/liburing-liburing-2.0/src/include -MD -MQ eval/io_latency.p/IoLatency.cpp.o -MF eval/io_latency.p/IoLatency.cpp.o.d -o eval/io_latency.p/IoLatency.cpp.o -c ../eval/IoLatency.cpp../eval/IoLatency.cpp: In function ‘void watchFunc()’:
../eval/IoLatency.cpp:45:17: error: ‘struct std::atomic<bool>’ has no member named ‘wait’
   45 |   readSubmitted.wait(false, std::memory_order_acquire);
      |                 ^~~~