Fix win64 warnings.

tools/win_dbghelp.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "windows.h"
 #include "win_dbghelp.h"
 #include <process.h>
@@ skipping 184 matching lines @@
     }
 
     return EXCEPTION_EXECUTE_HANDLER;
 }
 
 /** Sets the debugging variables. Input parameter is app location.
  *  e.g out\Debug\render_pdfs.exe
  *  This function expects the .pdb file to be in the same directory.
  */
 void setUpDebuggingFromArgs(const char* vargs0) {
-    int i = strlen(vargs0);
+    size_t i = strlen(vargs0);
 
     if (i >= 4 && _stricmp(vargs0 - 4, ".exe") == 0) {
         // Ignore .exe
         i -= 4;
     }
 
     int pos_period = i;
 
     // Find last \ in path - this is Windows!
     while (i >= 0 && vargs0[i] != '\\') {
@@ skipping 18 matching lines @@
 
     // cdb.exe is the app used to load the minidump which prints the callstack.
     char cdbExePath[MAX_PATH];
 #ifdef _WIN64
     sprintf(cdbExePath, "%s\\x64\\cdb.exe", SK_CDB_PATH);
 #else
     sprintf(cdbExePath, "%s\\cdb.exe", SK_CDB_PATH);
 #endif
     setCdbPath(cdbExePath);
 }