clang installation failure

I am running into an odd problem when I try to build llvm/clang 2.7
with --prefix=/sw/lib/llvm-2.7 and install it for packaging with...

make install DESTDIR=/sw/src/

...where /sw/lib/llvm-2.7 doesn't exist yet in the volume.
This fails with the error...

llvm[4]: ======= Finished Linking Release Executable clang (without symbols)
llvm[4]: Installing Release /sw/src/
make[4]: *** No rule to make target `/sw/lib/llvm-2.7/bin', needed by `/sw/src/'. Stop.
make[3]: *** [install] Error 1
make[2]: *** [install] Error 1
make[1]: *** [clang/.makeinstall] Error 2
make: *** [install] Error 1

However if I build with --prefix=/sw OR create /sw/lib/llvm-2.7/bin,
the installation succeeds. It appears that the Makefile's are leaky
and aren't honoring the DESTDIR in the case of installing the clang++
symlink. Any idea how to fix this in clang/tools/driver/CMakeLists.txt?