[PATCH] test: Make a start on a test suite for libLTO.

[Duncan P. N. Exon Smith]

> On 2015-Mar-19, at 16:21, Peter Collingbourne <peter at pcc.me.uk> wrote:
> 
> Hi dexonsmith,
> 
> This works in a similar way to the gold plugin tests. We search for a compatible
> linker on $PATH and use it to run tests against our just-built libLTO. To start
> with, test the just added opt level functionality.
> 
> http://reviews.llvm.org/D8472
> 
> Files:
>  cmake/config-ix.cmake
>  test/CMakeLists.txt
>  test/Makefile
>  test/lit.cfg
>  test/lit.site.cfg.in
>  test/tools/lto/lit.local.cfg
>  test/tools/lto/opt-level.ll
> 
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> <D8472.22320.patch>

This test suite will be pretty limited, since we have no control over
the version of `ld64`, and the LTO API (and how `ld64` calls it) has
changed a fair bit over time.  I think most tests should still be against
`llvm-lto`.

Nevertheless, this makes sense for checking that the clang driver options
make it through to libLTO.dylib.  LGTM.