[CMake] AddLLVM.cmake: Tweak the corner case that "check-all" doesn't have any tests.

"check-all" can be executed with 0 status, "check-all does nothing, no tools built."

LLVM_EXTERNAL_CLANG_BUILD=OFF LLVM_BUILD_TOOLS=OFF can reproduce this.
Oscar Fuentes reported this. Thank you.

llvm-svn: 171046

1 files changed, 11 insertions, 5 deletions

diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index cfb876e0763..516e02357c9 100755
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -279,11 +279,17 @@ function(add_lit_target target comment)
   foreach(param ${ARG_PARAMS})
     list(APPEND LIT_COMMAND --param ${param})
   endforeach()
-  add_custom_target(${target}
-    COMMAND ${LIT_COMMAND} ${ARG_DEFAULT_ARGS}
-    COMMENT "${comment}"
-    )
-  add_dependencies(${target} ${ARG_DEPENDS})
+  if( ARG_DEPENDS )
+    add_custom_target(${target}
+      COMMAND ${LIT_COMMAND} ${ARG_DEFAULT_ARGS}
+      COMMENT "${comment}"
+      )
+    add_dependencies(${target} ${ARG_DEPENDS})
+  else()
+    add_custom_target(${target}
+      COMMAND cmake -E echo "${target} does nothing, no tools built.")
+    message(STATUS "${target} does nothing.")
+  endif()
 endfunction()
 
 # A function to add a set of lit test suites to be driven through 'check-*' targets.