[CMake] Allow LLVM_TOOLCHAIN_TOOLS to be overridden

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247306 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Chris Bieneman

cmake/modules/AddLLVM.cmake

@@ -640,11 +640,12 @@ function(export_executable_symbols target)
   endif()
 endfunction()
 
-
-set (LLVM_TOOLCHAIN_TOOLS
-  llvm-ar
-  llvm-objdump
-  )
+if(NOT LLVM_TOOLCHAIN_TOOLS)
+  set (LLVM_TOOLCHAIN_TOOLS
+    llvm-ar
+    llvm-objdump
+    )
+endif()
 
 macro(add_llvm_tool name)
   if( NOT LLVM_BUILD_TOOLS )