FindHPX_Boost.cmake patch for OS X clang-based toolchain

clang-darwin.diff

diff --git a/cmake/FindHPX_Boost.cmake b/cmake/FindHPX_Boost.cmake
index e2ad0d9..f3977f0 100644
--- a/cmake/FindHPX_Boost.cmake
+++ b/cmake/FindHPX_Boost.cmake
@@ -57,7 +57,11 @@ macro(build_boost_libname BOOST_RAW_NAME)
     endif()
   elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang"
           OR "${CMAKE_CXX_COMPILER}" MATCHES "clang")
-    set(BOOST_COMPILER_VERSION "-clang")
+    if(APPLE)
+      set(BOOST_COMPILER_VERSION "-clang-darwin${BOOST_COMPILER_VERSION_NUMBER}")
+    else()
+      set(BOOST_COMPILER_VERSION "-clang")
+    endif()
   elseif(MSVC90)
     set(BOOST_COMPILER_VERSION "-vc90")
   elseif(MSVC10)