Fixes includes of endian.h on MacOS, see https://github.com/stbrumme/hash-library/pull/4.

diff --git a/crc32.cpp b/crc32.cpp
--- a/crc32.cpp
+++ b/crc32.cpp
@@ -7,8 +7,10 @@
 #include "crc32.h"
 
 // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 
diff --git a/keccak.cpp b/keccak.cpp
--- a/keccak.cpp
+++ b/keccak.cpp
@@ -7,8 +7,10 @@
 #include "keccak.h"
 
 // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 
diff --git a/md5.cpp b/md5.cpp
--- a/md5.cpp
+++ b/md5.cpp
@@ -6,8 +6,10 @@
 
 #include "md5.h"
 
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 
diff --git a/sha1.cpp b/sha1.cpp
--- a/sha1.cpp
+++ b/sha1.cpp
@@ -7,8 +7,10 @@
 #include "sha1.h"
 
 // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 
diff --git a/sha256.cpp b/sha256.cpp
--- a/sha256.cpp
+++ b/sha256.cpp
@@ -7,8 +7,10 @@
 #include "sha256.h"
 
 // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 
diff --git a/sha3.cpp b/sha3.cpp
--- a/sha3.cpp
+++ b/sha3.cpp
@@ -7,8 +7,10 @@
 #include "sha3.h"
 
 // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
-#ifndef _MSC_VER
-#include <endian.h>
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+#elif !defined(_MSC_VER)
+  #include <endian.h>
 #endif
 
 #include <iostream>