Fix libc build breakage by defining FSTYPENAMES before including

disklabel.h; broken originally by 1.87 of sys/disklabel.h, which
made the split between DKTYPENAMES and FSTYPENAMES.
Someone who knows disklabel.c: do we still need DKTYPENAMES to be
defined here now?

lib/libc/gen/disklabel.c

@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #define DKTYPENAMES
+#define FSTYPENAMES
 #include <sys/disklabel.h>
 
 #include <fcntl.h>