cmake: move two windows #defines to the main cmake file

We have a check for windows here anyway, let's move the defines here and we
can drop it in the common header file. And since on Unix HAVE_CONFIG_H is
always defined, we can drop the else condition too.

CMakeLists.txt

@@ -292,6 +292,8 @@ elseif (${CMAKE_SYSTEM_NAME} MATCHES "Windows")
     list (APPEND libs Wtsapi32 Userenv Wininet comsuppw Shlwapi)
 
     add_definitions (
+        /DSYSAPI_WIN32=1
+        /DWINAPI_MSWINDOWS=1
         /DWIN32
         /D_WINDOWS
         /D_CRT_SECURE_NO_WARNINGS

src/lib/common/common.h

@@ -18,13 +18,8 @@
 
 #pragma once
 
-#if defined(_WIN32)
-#	define SYSAPI_WIN32 1
-#	define WINAPI_MSWINDOWS 1
-#elif HAVE_CONFIG_H
+#if HAVE_CONFIG_H
 #	include "config.h"
-#else
-#	error "config.h missing"
 #endif
 
 // VC++ has built-in sized types