Autoconf updates

Move machine/endian.h to endian.h, use AC_HEADER_RESOLV over individual
header checks, and include prerequisites for netinet/ip.h check.

include/compat/endian.h

@@ -0,0 +1,48 @@
+/*
+ * Public domain
+ * endian.h compatibility shim
+ */
+
+#ifndef LIBCRYPTOCOMPAT_BYTE_ORDER_H_
+#define LIBCRYPTOCOMPAT_BYTE_ORDER_H_
+
+#if defined(_WIN32)
+
+#define LITTLE_ENDIAN  1234
+#define BIG_ENDIAN 4321
+#define PDP_ENDIAN	3412
+
+/*
+ * Use GCC and Visual Studio compiler defines to determine endian.
+ */
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define BYTE_ORDER LITTLE_ENDIAN
+#else
+#define BYTE_ORDER BIG_ENDIAN
+#endif
+
+#elif defined(HAVE_ENDIAN_H)
+#include_next <endian.h>
+
+#elif defined(__sun) || defined(_AIX) || defined(__hpux)
+#include <sys/types.h>
+#include <arpa/nameser_compat.h>
+
+#elif defined(__sgi)
+#include <standards.h>
+#include <sys/endian.h>
+
+#endif
+
+#ifndef __STRICT_ALIGNMENT
+#define __STRICT_ALIGNMENT
+#if defined(__i386)    || defined(__i386__)    || \
+    defined(__x86_64)  || defined(__x86_64__)  || \
+    defined(__s390__)  || defined(__s390x__)   || \
+    defined(__aarch64__)                       || \
+    ((defined(__arm__) || defined(__arm)) && __ARM_ARCH >= 6)
+#undef __STRICT_ALIGNMENT
+#endif
+#endif
+
+#endif