Include sys/sysctl.h in sysinfo.cpp for FreeBSD

[am11]

Regressed since #27048.

While this header is not required for GetSystemInfo by FreeBSD either, it is required for sysctl, sysctlnametomib and sysctlbyname:

https://www.freebsd.org/cgi/man.cgi?query=sysctlnametomib&apropos=0&sektion=0&manpath=FreeBSD+12.1-RELEASE&arch=default&format=html

build error:

[  5%] Building CXX object src/pal/src/CMakeFiles/coreclrpal.dir/misc/sysinfo.cpp.o
[  6%] Building CXX object src/md/compiler/CMakeFiles/mdcompiler_dac.dir/helper.cpp.o
[  6%] Building CXX object src/md/compiler/CMakeFiles/mdcompiler_crossgen.dir/emit.cpp.o
/home/am11/projects/dotnet/coreclr/src/pal/src/misc/sysinfo.cpp:382:10: error: use of undeclared identifier 'sysctlnametomib'
    rc = sysctlnametomib("vm.swap_info", mib, &length);
         ^
/home/am11/projects/dotnet/coreclr/src/pal/src/misc/sysinfo.cpp:390:18: error: use of undeclared identifier 'sysctl'
            rc = sysctl(mib, 3, &xsw, &length, NULL, 0);
                 ^
/home/am11/projects/dotnet/coreclr/src/pal/src/misc/sysinfo.cpp:599:30: error: use of undeclared identifier 'sysctlbyname'
        const bool success = sysctlbyname("hw.l3cachesize", &cacheSizeFromSysctl, &sz, nullptr, 0) == 0
                             ^
/home/am11/projects/dotnet/coreclr/src/pal/src/misc/sysinfo.cpp:600:16: error: use of undeclared identifier 'sysctlbyname'
            || sysctlbyname("hw.l2cachesize", &cacheSizeFromSysctl, &sz, nullptr, 0) == 0
               ^
/home/am11/projects/dotnet/coreclr/src/pal/src/misc/sysinfo.cpp:601:16: error: use of undeclared identifier 'sysctlbyname'
            || sysctlbyname("hw.l1dcachesize", &cacheSizeFromSysctl, &sz, nullptr, 0) == 0;
               ^
5 errors generated.
--- src/pal/src/CMakeFiles/coreclrpal.dir/misc/sysinfo.cpp.o ---
*** [src/pal/src/CMakeFiles/coreclrpal.dir/misc/sysinfo.cpp.o] Error code 1

make[2]: stopped in /usr/home/am11/projects/dotnet/coreclr/bin/obj/FreeBSD.x64.Release
1 error

cc @omajid, @wfurt: i was building master branches to run System.Diagnostics.Process tests in CoreFX and encountered this error. Otherwise build succeeds on FreeBSD 12.

[wfurt]

seems just like #27827 :)
I'm wondering if we should also guard rest of the code with HAVE_SYSCTLBYNAME instead of HAVE_SYSCTL so they are in balance.

[am11]

Ops, didn't realize #27819 is already fixing it. :)

HAVE_SYSCTLBYNAME instead of HAVE_SYSCTL

I think it makes sense as in this context, HAVE_SYSCTLBYNAME is more reliable macro to determine whether sys/sysctl.h should be included. It is also used in another file where sysctlnametomib is used.