one-off patch for CMake issue

[Vedant Kumar via llvm-commits]

+ Chris and Sylvestre as possible reviewers.

At first glance, it seems like the REMOVE_DUPLICATES operation isn't the only one we'd like to skip if LIB_NAMES is empty.

vedant

> On Jan 3, 2018, at 12:42 PM, Andy Bauer via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Hi,
> 
> Below is a patch for fixing a CMake issue I found:
> diff --git a/tools/llvm-shlib/CMakeLists.txt b/tools/llvm-shlib/CMakeLists.txt
> index b2109c8..a032540 100644
> --- a/tools/llvm-shlib/CMakeLists.txt
> +++ b/tools/llvm-shlib/CMakeLists.txt
> @@ -36,7 +36,9 @@ endif()
>  
>  add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB SONAME ${SOURCES})
>  
> -list(REMOVE_DUPLICATES LIB_NAMES)
> +if(LIB_NAMES)
> +  list(REMOVE_DUPLICATES LIB_NAMES)
> +endif()
>  if(("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux") OR (MINGW) OR (HAIKU)
>     OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "FreeBSD")
>     OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "DragonFly")
> 
> 
> 
> The CMake issue was that if LIB_NAMES is not defined then the list() method cannot remove duplicates. I encountered this when I enabled BUILD_SHARED_LIBS. Attached is my CMakeCache.txt that I encountered the issue with. The git SHA I'm working from is 
> 668a58d36b428217126511749a575aeb83fbc12f.
> 
> Please let me know if you need more information to properly review this patch.
> 
> Best,
> Andy
> 
> 
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