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.

[SVN r86167]

include/boost/predef/os/linux.h

@@ -26,13 +26,16 @@ http://www.boost.org/LICENSE_1_0.txt)
 
 #define BOOST_OS_LINUX BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
-#if defined(linux) || defined(__linux)
+#if !BOOST_PREDEF_DETAIL_OS_DETECTED && ( \
+    defined(linux) || defined(__linux) \
+    )
 #   undef BOOST_OS_LINUX
 #   define BOOST_OS_LINUX BOOST_VERSION_NUMBER_AVAILABLE
 #endif
 
 #if BOOST_OS_LINUX
 #   define BOOST_OS_LINUX_AVAILABLE
+#   include <boost/predef/detail/os_detected.h>
 #endif
 
 #define BOOST_OS_LINUX_NAME "Linux"