Avoid "Error: symbol `fatbinData' is already defined" caused by LTO when compiling with CUDA

[WEIXUEP]

Refer to the issue at #256, #340.

When attempting to build the palace application with CUDA support on Ubuntu 22.04, I encountered the same problem on two separate occasions:

1. In the test step of MFEM.
2. At the final build stage of palace

This issue can be resolved by taking two specific actions. First, when building with CUDA, I disable the test step of MFEM. Second, I add the appropriate CMake option during the final build step.
The following code snippet demonstrates how to add the necessary CMake option:

if(PALACE_WITH_CUDA)
  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-lto")
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-lto")
endif()