Replace StringFromInt with std::to_string

Updated version of #47. Android should support to_string now that
we use a modern version of libc++ when building.

Source/Core/Common/IniFile.cpp

@@ -93,7 +93,7 @@ void IniFile::Section::Set(const std::string& key, double newValue)
 
 void IniFile::Section::Set(const std::string& key, int newValue)
 {
-  Set(key, StringFromInt(newValue));
+  Set(key, std::to_string(newValue));
 }
 
 void IniFile::Section::Set(const std::string& key, s64 newValue)