Some details on cl.exe from MSDN:
cl.exe is a tool that controls the Microsoft C and C++ compilers and linker. cl.exe can be run only on operating systems that support Microsoft Visual Studio.
Likely it cannot find cl.exe because it doesn't know which SDK directory to find it in. This is related to the previous error you receive.
Could not find WindowsSDKDir variable from the registry. TargetFrameworkVersion or PlatformToolset may be set to an invalid version number.
The WindowsSDKDir variable defines where to find different compilation tools (including cl.exe). Either you don't have the SDK installed or your environment isn't configured properly.
Try to run the setenv first before your rebuild. (Related Link)
call "C:\Program Files\Microsoft SDKs\Windows\v7.1\bin\Setenv.cmd" /Release /x86
OR
call "C:\Program Files\Microsoft SDKs\Windows\v7.1\bin\Setenv.cmd" /Release /x64
If you're still running into problems provide some more information in your question about which SDK version you have installed.