mono @6.10.0.104: build fails on 10.8 and earlier

[chrstphrchvz (Christopher Chavez)]

mono currently does not build on ​10.8 or earlier due to use of features introduced in macOS 10.9:

mono-proclib.c:611:2: error: unknown type name 'task_vm_info_data_t'; did you mean 'task_info_data_t'?
        task_vm_info_data_t t_info;
        ^~~~~~~~~~~~~~~~~~~
        task_info_data_t
/usr/include/mach/task_info.h:85:19: note: 'task_info_data_t' declared here
typedef integer_t       task_info_data_t[TASK_INFO_MAX];
                        ^
mono-proclib.c:612:38: error: use of undeclared identifier 'TASK_VM_INFO_COUNT'
        mach_msg_type_number_t info_count = TASK_VM_INFO_COUNT;
                                            ^
mono-proclib.c:628:31: error: use of undeclared identifier 'TASK_VM_INFO'
                mach_ret = task_info (task, TASK_VM_INFO, (task_info_t)&t_info, &info_count);
                                            ^
mono-proclib.c:638:15: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.internal + t_info.compressed;
                      ~~~~~~^~~~~~~~~
mono-proclib.c:638:33: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.internal + t_info.compressed;
                                        ~~~~~~^~~~~~~~~~~
mono-proclib.c:640:15: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.resident_size;
                      ~~~~~~^~~~~~~~~~~~~~
mono-proclib.c:642:15: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.resident_size_peak;
                      ~~~~~~^~~~~~~~~~~~~~~~~~~
mono-proclib.c:644:15: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.virtual_size;
                      ~~~~~~^~~~~~~~~~~~~
mono-proclib.c:659:15: error: member reference base type 'task_info_data_t' (aka 'integer_t [1024]') is not a structure or union
                ret = t_info.compressed;
                      ~~~~~~^~~~~~~~~~~
9 errors generated.

Should a minimum OS version be set, or can these features be added to legacysupport somehow?