cmake: partial revert of BOOST_USE_VALGRIND when ALLOCATOR=libc

[cbodley]

the WITH_SYSTEM_BOOST binaries are not built with BOOST_USE_VALGRIND, so it probably isn't safe to define for the headers only

this flag is needed for teuthology testing, and the shaman builds use WITH_SYSTEM_BOOST=OFF. so the better fix is to enable WITH_BOOST_VALGRIND so BuildBoost.cmake will build the libraries with valgrind support and add -DBOOST_USE_VALGRIND to the necessary targets

this change was merged in ceph/ceph-build#1736

Fixes: https://tracker.ceph.com/issues/48963

Checklist

• References tracker ticket
• Updates documentation if necessary
• Includes tests for new functionality or reproducer for bug

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[cbodley]

uh oh, all tests in https://pulpito.ceph.com/cbodley-2021-02-03_16:14:08-rgw:verify-wip-48963-distro-basic-gibba/ (built with WITH_BOOST_VALGRIND) failed with this segfault:

*** Caught signal (Segmentation fault) **
 in thread 4433f700 thread_name:notif-worker0
 ceph version 17.0.0-403-g3c3a6519 (3c3a6519cce35d5643a9c05937d3661683fdac2f) quincy (dev)
 1: /lib64/libpthread.so.0(+0x12dd0) [0x1021ddd0]
 2: (spawn::detail::spawn_helper<boost::asio::executor_binder<void (*)(), boost::asio::strand<boost::asio::io_context::executor_type> >, rgw::notify::Manager::Manager(ceph::common::CephContext*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, rgw::sal::RGWRadosStore*)::{lambda(spawn::basic_yield_context<boost::asio::executor_binder<void (*)(), boost::asio::executor> >)#1}, boost::context::basic_protected_fixedsize_stack<rgw::notify::Manager::Manager(ceph::common::CephContext*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, rgw::sal::RGWRadosStore*)::{lambda(spawn::basic_yield_context<boost::asio::executor_binder<void (*)(), boost::asio::executor> >)#1}::stack_traits> >::operator()()+0x63) [0x59b23f3]
 3: (boost::asio::detail::executor_op<spawn::detail::spawn_helper<boost::asio::executor_binder<void (*)(), boost::asio::strand<boost::asio::io_context::executor_type> >, rgw::notify::Manager::Manager(ceph::common::CephContext*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, rgw::sal::RGWRadosStore*)::{lambda(spawn::basic_yield_context<boost::asio::executor_binder<void (*)(), boost::asio::executor> >)#1}, boost::context::basic_protected_fixedsize_stack<rgw::notify::Manager::Manager(ceph::common::CephContext*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, rgw::sal::RGWRadosStore*)::{lambda(spawn::basic_yield_context<boost::asio::executor_binder<void (*)(), boost::asio::executor> >)#1}::stack_traits> >, std::allocator<void>, boost::asio::detail::scheduler_operation>::do_complete(void*, std::allocator<void>*, boost::system::error_code const&, unsigned long)+0xa8) [0x59b2568]
 4: (boost::asio::detail::strand_executor_service::invoker<boost::asio::io_context::executor_type const>::operator()()+0x8d) [0x5313e1d]
 5: (boost::asio::detail::executor_op<boost::asio::detail::strand_executor_service::invoker<boost::asio::io_context::executor_type const>, std::allocator<void>, boost::asio::detail::scheduler_operation>::do_complete(void*, boost::asio::detail::scheduler_operation*, boost::system::error_code const&, unsigned long)+0x99) [0x53140a9]
 6: (boost::asio::detail::scheduler::run(boost::system::error_code&)+0x4f2) [0x1b57a2]
 7: (std::thread::_State_impl<std::thread::_Invoker<std::tuple<rgw::notify::Manager::Manager(ceph::common::CephContext*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, rgw::sal::RGWRadosStore*)::{lambda()#2}> > >::_M_run()+0x46) [0x59af106]
 8: /lib64/libstdc++.so.6(+0xc2a33) [0x111dca33]
 9: /lib64/libpthread.so.0(+0x82de) [0x102132de]

seeing if i can reproduce it myself

[cbodley]

the segfault was due to radosgw's cmake not forwarding the BOOST_USE_VALGRIND definition from boost::context

fixed in #39279