CMake: Fix sphinx build with standalone clang

[tstellar]

Summary

This code is copied from llvm/cmake/config-ix.cmake. Would it be better
to refactor this code and put it in
llvm/cmake/modules/AddSphinxTarget.cmake ?

[tstellar]

Remove redundant find_package(Sphinx)

[mgorny]

See also: D23758, for SphInx + doxygen + relevant options.

[beanz]

I think putting this into AddSphinxTarget.cmake would be a better way to handle it. Also I have one small inline comment.

CMakeLists.txt

177

If tis code can be run more than once you also need to add AND NOT TARGET sphinx to the condition here.

[tstellar]

Move most logic into AddSphinxTarget.cmake in the llvm tree.

[tstellar]

Ping.

[beanz]

LGTM.

CMakeLists.txt

if(LLVM_LIT)
       if( WIN32 AND NOT CYGWIN )
         set(LLVM_LIT_TOOLS_DIR "" CACHE PATH "Path to GnuWin32 tools")
       endif()
     else()
       set(LLVM_INCLUDE_TESTS OFF)
     endif()
   endif()
 
+  if (LLVM_ENABLE_SPHINX)
+    message(STATUS "Sphinx enabled.")
+    find_package(Sphinx REQUIRED)
+    if (LLVM_BUILD_DOCS)
+      add_custom_target(sphinx ALL)
+    endif()
+  else()
+    message(STATUS "Sphinx disabled.")
+  endif()
+
   set( CLANG_BUILT_STANDALONE 1 )
   set(BACKEND_PACKAGE_STRING "LLVM ${LLVM_PACKAGE_VERSION}")
 else()
   set(BACKEND_PACKAGE_STRING "${PACKAGE_STRING}")
 endif()
 
 # Make sure that our source directory is on the current cmake module path so that
 # we can include cmake files from this directory.