Port to Clang 20

[asantagata]

Ported to Clang 20 as described in #191

[tpatki]

@asantagata

• We need to change the clang version in CI as well, so your tests pass here. That change is here.
• You also need to change the CMakeLists to ensure that Clang 20.0 is the pinned version instead of Clang18. That change is here:

  PerfFlowAspect/src/c/CMakeLists.txt

  Lines 8 to 15 in 2af15c3

  	# Fail if using Clang < 18.0
  	if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
  	if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0)
  	message(FATAL_ERROR "Clang++ version must be equal to 18.0!")
  	endif()
  	else()
  	message(FATAL_ERROR "Unsupported CXX compiler: please use Clang == 18.0")
  	endif()

Could you fix these in this PR as well?