[lit] Add missing split-file dependency

There was a recent patch that added in some tests to the lit test suite
that use split-file. An explicit dependency in CMake was not added,
which led to check-lit not working if being run without doing a full
build first. This patch explicitly adds the dependency inside the CMake
file to fix this configuration.

Author: boomanaiden154

CMakeLists.txt

@@ -22,7 +22,7 @@ add_custom_target(prepare-check-lit
 # Add rules for lit's own test suite
 add_lit_testsuite(check-lit "Running lit's tests"
   ${CMAKE_CURRENT_BINARY_DIR}
-  DEPENDS "FileCheck" "not" "prepare-check-lit"
+  DEPENDS "FileCheck" "not" "split-file" "prepare-check-lit"
 )
 
 # For IDEs