[CMake] rpath trouble on macosx: cmake 2.8.9 ignores INSTALL_NAME_DIR and INSTALL_RPATH?

[Dan Kegel]

Howdy!
I'm using 2.8.9 installed on MacOSX using macports, and am trying to get
a minimal example of rpath working.

Doing it without cmake works fine; see
  http://kegel.com/macosx/rpath/demo.txt
which just does
  gcc -shared foo.c -install_name @rpath/foo.so -o foo.so
  gcc -Wl,-rpath $OTHERDIR x.c foo.so
and works fine.

But doing it with cmake eludes me.  Here's what I'm trying:
  http://kegel.com/macosx/rpath/demo2.txt
  http://kegel.com/macosx/rpath/CMakeLists.txt
That CMakeLists.txt is just

cmake_minimum_required(VERSION 2.8)
set(MYLIBDIR "${CMAKE_SOURCE_DIR}/otherdir")

add_library(foo SHARED foo.c)
set_target_properties(foo PROPERTIES INSTALL_NAME_DIR "@rpath")

add_executable(x x.c)
set_target_properties(
    x
    PROPERTIES
    BUILD_WITH_INSTALL_RPATH 1
    INSTALL_RPATH ${MYLIBDIR}
)
target_link_libraries(x foo)

When I run demo2.txt, it does

/usr/bin/gcc   -dynamiclib -Wl,-headerpad_max_install_names   -o
libfoo.dylib -install_name /Users/dank/rpath/btmp/libfoo.dylib
CMakeFiles/foo.dir/foo.c.o
/usr/bin/gcc    -o CMakeFiles/x.dir/x.c.o   -c /Users/dank/rpath/x.c
/usr/bin/gcc   -Wl,-search_paths_first
-Wl,-headerpad_max_install_names   CMakeFiles/x.dir/x.c.o  -o x
libfoo.dylib

and it appears to have totally ignored INSTALL_RPATH,
so naturally running x fails with
dyld: Library not loaded: /Users/dank/rpath/btmp/libfoo.dylib

Can I buy a clue, please?