Nearly complete rewrite of cgpt tool.

cgpt/endian.h

+#ifndef VBOOT_REFERENCE_UTILITY_CGPT_ENDIAN_H_
+#define VBOOT_REFERENCE_UTILITY_CGPT_ENDIAN_H_
+
+// Newer distros already have this. For those that don't, we add it here.
+#include <endian.h>
+
+#ifndef le16toh
+
+# include <byteswap.h>
+
+# if __BYTE_ORDER == __LITTLE_ENDIAN
+#  define htobe16(x) __bswap_16 (x)
+#  define htole16(x) (x)
+#  define be16toh(x) __bswap_16 (x)
+#  define le16toh(x) (x)
+
+#  define htobe32(x) __bswap_32 (x)
+#  define htole32(x) (x)
+#  define be32toh(x) __bswap_32 (x)
+#  define le32toh(x) (x)
+
+#  define htobe64(x) __bswap_64 (x)
+#  define htole64(x) (x)
+#  define be64toh(x) __bswap_64 (x)
+#  define le64toh(x) (x)
+# else
+#  define htobe16(x) (x)
+#  define htole16(x) __bswap_16 (x)
+#  define be16toh(x) (x)
+#  define le16toh(x) __bswap_16 (x)
+
+#  define htobe32(x) (x)
+#  define htole32(x) __bswap_32 (x)
+#  define be32toh(x) (x)
+#  define le32toh(x) __bswap_32 (x)
+
+#  define htobe64(x) (x)
+#  define htole64(x) __bswap_64 (x)
+#  define be64toh(x) (x)
+#  define le64toh(x) __bswap_64 (x)
+# endif
+
+#endif
+#endif  // VBOOT_REFERENCE_UTILITY_CGPT_ENDIAN_H_