Add llvm-dwp to LLVM_TOOLCHAIN_TOOLS

[hans]

Summary

since it qualifies as a toolchain tool rather than "internal llvm tool".
This will make it part of builds which set the
LLVM_INSTALL_TOOLCHAIN_ONLY cmake option, such as the Windows installer.

This came up in https://llvm.discourse.group/t/llvm-dwp-utility-on-windows/5866/

[dblaikie]

Sounds good, thanks!

llvm/cmake/modules/AddLLVM.cmake

function(export_executable_symbols_for_plugins target)
   endif()
 endfunction()
 
 if(NOT LLVM_TOOLCHAIN_TOOLS)
   set (LLVM_TOOLCHAIN_TOOLS
     llvm-ar
     llvm-cov
     llvm-cxxfilt
+    llvm-dwp
     llvm-ranlib
     llvm-lib
     llvm-ml
     llvm-nm
     llvm-objcopy
     llvm-objdump
     llvm-rc
     llvm-readobj