[compiler-rt][CMake] Pass down LLVM_LIT_ARGS in runtime build

We should also pass down the LLVM_LIT_ARGS in runtime build mode,
so that the runtime tests can be well controlled as well.

We actually passed this down in clang/runtime/CMakeLists.txt
But not for calls from llvm/runtime/CMakeLists.txt.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D83565

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

@@ -250,6 +250,7 @@ function(llvm_ExternalProject_Add name source_dir)
                -DLLVM_HAVE_LINK_VERSION_SCRIPT=${LLVM_HAVE_LINK_VERSION_SCRIPT}
                -DLLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO=${LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO}
                -DLLVM_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
+               -DLLVM_LIT_ARGS=${LLVM_LIT_ARGS}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}