compiler: Define NO_RETURN for MSVC.

To prevent warnings such as "Not all control paths return a value",
we should define NO_RETURN for MSVC.

Currently for gcc, we add NO_RETURN at the end of function declaration.
But for MSVC, "__declspec(noreturn)" is needed at the beginning of function
declaration. So this commit moves NO_RETURN to the beginning of the function
declaration as it works with gcc and clang too.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>