What is Kernel32?

[Sixte]

I just tried to compile a project relying on the windows API, in particular 
"VirtualProtect", therefore the function gets declared with a "windows.h" 
header. Nim went trough, but gcc stopped because of a missing "Kernel32". 
Indeed, the C intermediate contains an #include "Kernel32" ( I'd expect a 
"Kernel32.h" , but there is no such extension). So, where do I get the file 
from or should "windows.h" be avoided?