Add support for building Sphinx documentation when being built inside LLVM source tree and using CMake.

Patch by Dan Liew <daniel.liew@imperial.ac.uk>!

llvm-svn: 206662

lld/CMakeLists.txt

@@ -180,3 +180,5 @@ add_subdirectory(test)
 if (LLVM_INCLUDE_TESTS AND NOT LLD_BUILT_STANDALONE)
   add_subdirectory(unittests)
 endif()
+
+add_subdirectory(docs)

lld/docs/CMakeLists.txt

@@ -0,0 +1,8 @@
+if (LLVM_ENABLE_SPHINX)
+  if (SPHINX_FOUND)
+    include(AddSphinxTarget)
+    if (${SPHINX_OUTPUT_HTML})
+      add_sphinx_target(html lld)
+    endif()
+  endif()
+endif()