configure: auto-generate a config-host.h

Don't have all these special cases to convert a .mak to a .h define,
just generate it from the configure script instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/os/os.h b/os/os.h
index f33a7cd..ef9f91f 100644
--- a/os/os.h
+++ b/os/os.h
@@ -56,7 +56,7 @@
 #include <scsi/sg.h>
 #endif
 
-#ifdef CONFIG_STRSEP
+#ifndef CONFIG_STRSEP
 #include "../lib/strsep.h"
 #endif