[cmake] Start making LLVM_LIBDIR_SUFFIX effective by adding it to
*numerous* places where it was missing in the CMake build. The primary
change here is that the suffix is now actually used for all of the lib
directories in the LLVM project's CMake. The various subprojects still
need similar treatment.

This is the first of a series of commits to try to make LLVM's cmake
effective in a multilib Linux installation. I don't think many people
are seriously using this variable so I'm hoping the fallout will be
minimal. A somewhat unfortunate consequence of the nature of these
commits is that until I land all of them, they will in part make the
brokenness of our multilib support more apparant. At the end, things
should actually work.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224919 91177308-0d34-0410-b5e6-96231b3b80d8
[cmake] Push LLVM_LIBDIR_SUFFIX through to the LLVMConfig.cmake file
that is used by other projects to build against LLVM. This will allow
subsequent patches to them to use LLVM_LIBDIR_SUFFIX, both when built as
part of the larger LLVM build an as part of a standalone build against
an installed set of LLVM libraries.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224920 91177308-0d34-0410-b5e6-96231b3b80d8
[cmake] Teach the llvm-config program to respect LLVM_LIBDIR_SUFFIX.

For this to work, we have to encode it in the build variables and use it
from llvm-config.cpp. I've tried to do this reasonably cleanly, but the
code for llvm-config.cpp is pretty strange. However, with this,
llvm-config stops giving the wrong answer when using LLVM_LIBDIR_SUFFIX.

Note that the configure+make build just sets this to an empty string as
that build system has zero support for multilib of any form. I'm not
planning to add support there either, but this should leave a path for
anyone that wanted to.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224921 91177308-0d34-0410-b5e6-96231b3b80d8
[multilib] Add support to the autoconf build to substitute
a CLANG_LIBDIR_SUFFIX variable. This is necessary before I can add
support for using that variable to CMake and the C++ code in Clang, and
the autoconf build system does all substitutions in the LLVM tree.

As mentioned before, I'm not planning to add actual multilib support to
the autoconf build, just enough stubs for it to keep playing nicely with
the CMake build once that one has support.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224922 91177308-0d34-0410-b5e6-96231b3b80d8