[PATCH] Fix test-release.sh to use DESTDIR

[Dan Liew]

> I did a 64-bit build on my Linux box and everything built and passed
> tests correctly.
>
> LLVM_INSTALL_PREFIX is set to /usr/local in LLVMConfig.cmake in the
> tarball, so that seems right too.
>
> Please go ahead and commit.

Great. Thanks for the review.

Committed in r242187

On a related note is this the version that will be used for the 3.7
release? I seem remember there being a patch floating around in
phabricator for this script to use CMake to do the build instead.

Thanks,
Dan.