lib/Header: Fix Visual Studio builds

[tstellar]

Summary

This is a follow up to r355253, which inadvertently broke Visual
Studio builds by trying to copy files from CMAKE_CFG_INTDIR.

See https://reviews.llvm.org/D58537#inline-532492

[smeenai]

LGTM

This would break if someone does a debug and release build simultaneously, the copies occur simultaneously and the filesystem gets unhappy, That seems fairly contrived though, and this is also restoring the behavior before your previous change.

lib/Headers/CMakeLists.txt

set(cuda_wrapper_files
   cuda_wrappers/complex
   cuda_wrappers/new
 )
 
 set(ppc_wrapper_files
   ppc_wrappers/mmintrin.h
 )
 
-set(output_dir ${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}/include)
+set(output_dir ${CMAKE_CURRENT_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}/include)
 set(out_files)
 
 function(copy_header_to_output_dir src_dir file)
   set(src ${src_dir}/${file})
   set(dst ${output_dir}/${file})
   add_custom_command(OUTPUT ${dst}
     DEPENDS ${src}
     COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}