Address endian compile errors for OSX in the cases where sys/param.h was

include ahead of the predef headers. The solution was to: use the OSX
machine/endian.h header, and only allow a single OS to be detected at
once. Test cases added for both conditions on OSX.

include/boost/predef/os/macos.h

@@ -31,8 +31,10 @@ http://www.boost.org/LICENSE_1_0.txt)
 
 #define BOOST_OS_MACOS BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
-#if defined(macintosh) || defined(Macintosh) || \
-    (defined(__APPLE__) && defined(__MACH__))
+#if !BOOST_PREDEF_DETAIL_OS_DETECTED && ( \
+    defined(macintosh) || defined(Macintosh) || \
+    (defined(__APPLE__) && defined(__MACH__)) \
+    )
 #   undef BOOST_OS_MACOS
 #   if !defined(BOOST_OS_MACOS) && defined(__APPLE__) && defined(__MACH__)
 #       define BOOST_OS_MACOS BOOST_VERSION_NUMBER(10,0,0)
@@ -44,6 +46,7 @@ http://www.boost.org/LICENSE_1_0.txt)
 
 #if BOOST_OS_MACOS
 #   define BOOST_OS_MACOS_AVAILABLE
+#   include <boost/predef/detail/os_detected.h>
 #endif
 
 #define BOOST_OS_MACOS_NAME "Mac OS"