libdiskfs: avoid problematic internal constant names

AIX defines some of these constants in its C header files.

src/libdiskfs/ext2.h

@@ -27,6 +27,39 @@ enum
 
 	NAMELEN = 255,
 
+	/* some systems have these defined */
+	#undef IEXEC
+	#undef IWRITE
+	#undef IREAD
+	#undef ISVTX
+	#undef ISGID
+	#undef ISUID
+	#undef IFMT
+	#undef IFIFO
+	#undef IFCHR
+	#undef IFDIR
+	#undef IFBLK
+	#undef IFREG
+	#undef IFLNK
+	#undef IFSOCK
+	#undef IFWHT
+
+	#define IEXEC	EXT2_IEXEC
+	#define IWRITE	EXT2_IWRITE
+	#define IREAD	EXT2_IREAD
+	#define ISVTX	EXT2_ISVTX
+	#define ISGID	EXT2_ISGID
+	#define ISUID	EXT2_ISUID
+	#define IFMT	EXT2_IFMT
+	#define IFIFO	EXT2_IFIFO
+	#define IFCHR	EXT2_IFCHR
+	#define IFDIR	EXT2_IFDIR
+	#define IFBLK	EXT2_IFBLK
+	#define IFREG	EXT2_IFREG
+	#define IFLNK	EXT2_IFLNK
+	#define IFSOCK	EXT2_IFSOCK
+	#define IFWHT	EXT2_IFWHT
+
 	/* permissions in Inode.mode */
 	IEXEC = 00100,
 	IWRITE = 0200,

src/libdiskfs/ffs.h

@@ -72,6 +72,39 @@ enum
 	NDADDR = 12,
 	NIADDR = 3,
 
+	/* some systems have these defined */
+	#undef IEXEC
+	#undef IWRITE
+	#undef IREAD
+	#undef ISVTX
+	#undef ISGID
+	#undef ISUID
+	#undef IFMT
+	#undef IFIFO
+	#undef IFCHR
+	#undef IFDIR
+	#undef IFBLK
+	#undef IFREG
+	#undef IFLNK
+	#undef IFSOCK
+	#undef IFWHT
+
+	#define IEXEC	FFS_IEXEC
+	#define IWRITE	FFS_IWRITE
+	#define IREAD	FFS_IREAD
+	#define ISVTX	FFS_ISVTX
+	#define ISGID	FFS_ISGID
+	#define ISUID	FFS_ISUID
+	#define IFMT	FFS_IFMT
+	#define IFIFO	FFS_IFIFO
+	#define IFCHR	FFS_IFCHR
+	#define IFDIR	FFS_IFDIR
+	#define IFBLK	FFS_IFBLK
+	#define IFREG	FFS_IFREG
+	#define IFLNK	FFS_IFLNK
+	#define IFSOCK	FFS_IFSOCK
+	#define IFWHT	FFS_IFWHT
+
 	/* permissions in Inode.mode */
 	IEXEC = 00100,
 	IWRITE = 0200,