long.ToString("x16") returns a useless string.
As a consequence the Number_ToString_Test in systemlib2.sln fails.
 
The problem does not exist on the emulator, just on ARM targets.
 
Reason:
The reason is a wrong format string in \CLR\Libraries\CorLib\corlib_native_System_Number.cpp.
In line 62 & 68, formatStr must be replaced by "%llX".