Fix cycles_test link error on macOS due to boost python in new 3.5 libraries

The executable would get boost python linking in when not needed, and even when
linking to Python libraries there were still unresolved symbols. Instead split
off boost python libraries and link them only where needed.

build_files/cmake/platform/platform_apple.cmake

@@ -260,7 +260,12 @@ if(WITH_BOOST)
   endif()
   find_package(Boost COMPONENTS ${_boost_FIND_COMPONENTS})
 
+  # Boost Python is separate to avoid linking Python into tests that don't need it.
   set(BOOST_LIBRARIES ${Boost_LIBRARIES})
+  if(WITH_USD AND USD_PYTHON_SUPPORT)
+    set(BOOST_PYTHON_LIBRARIES ${Boost_PYTHON${PYTHON_VERSION_NO_DOTS}_LIBRARY})
+    list(REMOVE_ITEM BOOST_LIBRARIES ${BOOST_PYTHON_LIBRARIES})
+  endif()
   set(BOOST_INCLUDE_DIR ${Boost_INCLUDE_DIRS})
   set(BOOST_DEFINITIONS)
 

build_files/cmake/platform/platform_unix.cmake

@@ -407,8 +407,13 @@ if(WITH_BOOST)
     mark_as_advanced(Boost_INCLUDE_DIR)  # why doesn't boost do this?
   endif()
 
-  set(BOOST_INCLUDE_DIR ${Boost_INCLUDE_DIRS})
+  # Boost Python is separate to avoid linking Python into tests that don't need it.
   set(BOOST_LIBRARIES ${Boost_LIBRARIES})
+  if(WITH_USD AND USD_PYTHON_SUPPORT)
+    set(BOOST_PYTHON_LIBRARIES ${Boost_PYTHON${PYTHON_VERSION_NO_DOTS}_LIBRARY})
+    list(REMOVE_ITEM BOOST_LIBRARIES ${BOOST_PYTHON_LIBRARIES})
+  endif()
+  set(BOOST_INCLUDE_DIR ${Boost_INCLUDE_DIRS})
   set(BOOST_LIBPATH ${Boost_LIBRARY_DIRS})
   set(BOOST_DEFINITIONS "-DBOOST_ALL_NO_LIB")
 

build_files/cmake/platform/platform_win32.cmake

@@ -575,7 +575,7 @@ if(WITH_BOOST)
     )
     if (EXISTS ${BOOST_34_TRIGGER_FILE})
       if(WITH_USD)
-        set(BOOST_LIBRARIES ${BOOST_LIBRARIES}
+        set(BOOST_PYTHON_LIBRARIES
           debug ${BOOST_LIBPATH}/${BOOST_PREFIX}boost_python310-${BOOST_DEBUG_POSTFIX}.lib
           optimized ${BOOST_LIBPATH}/${BOOST_PREFIX}boost_python310-${BOOST_POSTFIX}.lib
         )

source/blender/io/usd/CMakeLists.txt

@@ -123,6 +123,7 @@ set(LIB
 
 list(APPEND LIB
   ${BOOST_LIBRARIES}
+  ${BOOST_PYTHON_LIBRARIES}
   ${PYTHON_LIBRARIES}
 )