Update the ELFOSABI_* constants.

Two new operating systems have been added in the meantime.
ELFOSABI_FENIXOS that uses value 16 (published in the latest draft) and
ELFOSABI_CLOUDABI that uses value 17 (to be published in the next draft).

sys/sys/elf_common.h

@@ -169,6 +169,8 @@ typedef struct {
 #define	ELFOSABI_OPENVMS	13	/* Open VMS */
 #define	ELFOSABI_NSK		14	/* HP Non-Stop Kernel */
 #define	ELFOSABI_AROS		15	/* Amiga Research OS */
+#define	ELFOSABI_FENIXOS	16	/* FenixOS */
+#define	ELFOSABI_CLOUDABI	17	/* Nuxi CloudABI */
 #define	ELFOSABI_ARM		97	/* ARM */
 #define	ELFOSABI_STANDALONE	255	/* Standalone (embedded) application */