[debugserver] Fix sign comparison warning.

[brucem]

Summary

Comparing m_page_size against kInvalidPageSize was resulting in
a warning about comparing integers with different signs. Since
kInvalidPageSize isn't used anywhere outside of MachVMMemory.cpp,
we can readily transform it into a static const vm_size_t with
the correct value to avoid the sign comparison warnings.

tools/debugserver/source/MacOSX/MachVMMemory.h

 
 #include "DNBDefs.h"
 #include "DNBError.h"
 #include <mach/mach.h>
 
 class MachVMMemory
 {
 public:
-    enum { kInvalidPageSize = ~0 };
     MachVMMemory();
     ~MachVMMemory();
     nub_size_t Read(task_t task, nub_addr_t address, void *data, nub_size_t data_count);
     nub_size_t Write(task_t task, nub_addr_t address, const void *data, nub_size_t data_count);
     nub_size_t PageSize(task_t task);
     nub_bool_t GetMemoryRegionInfo(task_t task, nub_addr_t address, DNBRegionInfo *region_info);
 #if defined (HOST_VM_INFO64_COUNT)
     nub_bool_t GetMemoryProfile(DNBProfileDataScanType scanType, task_t task, struct task_basic_info ti, cpu_type_t cputype, nub_process_t pid, vm_statistics64_data_t &vminfo, uint64_t &physical_memory, mach_vm_size_t &rprvt, mach_vm_size_t &rsize, mach_vm_size_t &vprvt, mach_vm_size_t &vsize, mach_vm_size_t &dirty_size, mach_vm_size_t &purgeable, mach_vm_size_t &anonymous);

tools/debugserver/source/MacOSX/MachVMMemory.cpp

 #include "MachVMMemory.h"
 #include "MachVMRegion.h"
 #include "DNBLog.h"
 #include <mach/mach_vm.h>
 #include <mach/shared_region.h>
 #include <sys/sysctl.h>
 #include <dlfcn.h>
 
+static const vm_size_t kInvalidPageSize = ~0;
+
 MachVMMemory::MachVMMemory() :
     m_page_size    (kInvalidPageSize),
     m_err        (0)
 {
 }
 
 MachVMMemory::~MachVMMemory()
 {