Bug 1256464 - Use LPSTR instead of LPVOID to avoid C4477 on VS2015; r=froydnj

Without this change, Visual Studio 2015 complains:

mozglue/misc/StackWalk.cpp(261): warning C4477: 'fprintf' : format
string '%s' requires an argument of type 'char *', but variadic argument
2 has type 'LPVOID'

MozReview-Commit-ID: HIAs5L57Nd1

--HG--
extra : rebase_source : 1ac50c03c4d6b14e22f3d55aca026fce15565f5c

mozglue/misc/StackWalk.cpp

@@ -247,7 +247,7 @@ CRITICAL_SECTION gDbgHelpCS;
 static void
 PrintError(const char* aPrefix)
 {
-  LPVOID lpMsgBuf;
+  LPSTR lpMsgBuf;
   DWORD lastErr = GetLastError();
   FormatMessageA(
     FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,