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/other/endian.h

@@ -11,6 +11,7 @@ http://www.boost.org/LICENSE_1_0.txt)
 #include <boost/predef/version_number.h>
 #include <boost/predef/make.h>
 #include <boost/predef/library/c/gnu.h>
+#include <boost/predef/os/macos.h>
 #include <boost/predef/os/bsd.h>
 
 /*`
@@ -48,17 +49,22 @@ information and acquired knowledge:
 #define BOOST_ENDIAN_LITTLE_WORD BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 /* GNU libc provides a header defining __BYTE_ORDER, or _BYTE_ORDER.
+ * And some OSs provide some for of endian header also.
  */
 #if !BOOST_ENDIAN_BIG_BYTE && !BOOST_ENDIAN_BIG_WORD && \
     !BOOST_ENDIAN_LITTLE_BYTE && !BOOST_ENDIAN_LITTLE_WORD
 #   if BOOST_LIB_C_GNU
 #       include <endian.h>
 #   else
-#       if BOOST_OS_BSD
-#           if BOOST_OS_BSD_OPEN
-#               include <machine/endian.h>
-#           else
-#               include <sys/endian.h>
+#       if BOOST_OS_MACOS
+#           include <machine/endian.h>
+#       else
+#           if BOOST_OS_BSD
+#               if BOOST_OS_BSD_OPEN
+#                   include <machine/endian.h>
+#               else
+#                   include <sys/endian.h>
+#               endif
 #           endif
 #       endif
 #   endif