[CMake] Avoid clang-tablegen-targets dependency when building sphinx …

…docs (experimental)

Proposal to fix bot
http://lab.llvm.org:8011/builders/lldb-sphinx-docs/builds/1564/steps/cmake-configure/logs/stdio

Patch by: Stefan Gränitz

Differential revision: https://reviews.llvm.org/D59232

llvm-svn: 355887

lldb/cmake/modules/AddLLDB.cmake

@@ -93,7 +93,7 @@ function(add_lldb_library name)
   # Hack: only some LLDB libraries depend on the clang autogenerated headers,
   # but it is simple enough to make all of LLDB depend on some of those
   # headers without negatively impacting much of anything.
-  if(NOT LLDB_BUILT_STANDALONE)
+  if(NOT LLDB_BUILT_STANDALONE AND NOT LLVM_ENABLE_SPHINX)
     add_dependencies(${name} clang-tablegen-targets)
   endif()