close_range is missing on FreeBSD 10

Start with libs/process/src/posix/close_handles.cpp, where Process V2 calls close_range and FreeBSD 10 reports it as undeclared. Check the surrounding platform-specific logic and the reported build configuration, then verify that Boost Process builds successfully on FreeBSD 10 without the close_range errors.

We're trying to build Boost 1.86.0 for FreeBSD 10 and getting the following error:

".../i686-pc-freebsd10.0_gcc7.3.0/bin/i686-pc-freebsd10.0-g++"   -fvisibility-inlines-hidden -static-libgcc -static-libstdc++ -static-libgcc -static-libstdc++ -std=gnu++14 -fPIC   -O2 -DNDEBUG -DBOOST_CHRONO_THREAD_DISABLED -m32 -pthread -O3 -finline-functions -Wno-inline -Wall -fvisibility=hidden -march=i686  -DBOOST_ALL_NO_LIB=1 -DBOOST_ASIO_NO_DEPRECATED -DBOOST_ATOMIC_STATIC_LINK=1 -DBOOST_FILESYSTEM_STATIC_LINK=1 -DBOOST_PROCESS_SOURCE=1 -DNDEBUG   -I"."  -c -o ".../boost/bin.v2/libs/process/build/gcc-7/release/x86_32/link-static/target-os-freebsd/threading-multi/visibility-hidden/posix/close_handles.o" "libs/process/src/posix/close_handles.cpp"

libs/process/src/posix/close_handles.cpp: In function 'void boost::process::v2::posix::detail::close_all(const std::vector<int>&, boost::system::error_code&)':
libs/process/src/posix/close_handles.cpp:125:15: error: '::close_range' has not been declared
             ::close_range(0, whitelist.front() - 1, 0);
               ^~~~~~~~~~~
libs/process/src/posix/close_handles.cpp:125:15: note: suggested alternative: 'close_all'
             ::close_range(0, whitelist.front() - 1, 0);
               ^~~~~~~~~~~
               close_all
libs/process/src/posix/close_handles.cpp:135:19: error: '::close_range' has not been declared
                 ::close_range(mine + 1, next - 1, 0);
                   ^~~~~~~~~~~
libs/process/src/posix/close_handles.cpp:135:19: note: suggested alternative: 'close_all'
                 ::close_range(mine + 1, next - 1, 0);
                   ^~~~~~~~~~~
                   close_all

It seems this is due to code that is used only in Process V2. Is there a way to fallback to Process V1?