Bump LLVM to 18.1.8

[kd-11]

No description provided.

[Megamouse]

• See 16.0.1 in BUILDING.md
• See 16.0.1 in get_keys_windows.sh

[Megamouse]

Needs conflict solved

[kd-11]

It needs a lot done actually. I'll try and fix it before end of year.

[digant73]

Downloaded from the llvm official repo both the source and pre-compiled llvm 18.1.8 version.
In 3rdparty/llvm/CMakeLists.txt, the following changes need to be applied:

find_package(LLVM 16.0 CONFIG)

in

find_package(LLVM 18.1 CONFIG)

and

if (LLVM_VERSION VERSION_LESS 16)
    message(FATAL_ERROR "Found LLVM version ${LLVM_VERSION}. Required version 16 or above. \
        Enable BUILD_LLVM option to build LLVM from included as a git submodule.")

in

if (LLVM_VERSION VERSION_LESS 18.1)
    message(FATAL_ERROR "Found LLVM version ${LLVM_VERSION}. Required version 18.1 or above. \
        Enable BUILD_LLVM option to build LLVM from included as a git submodule.")

I could test it under Windows 11:

• with CMake: with the above changes, I was able to successfully compile and build the application.
• with Visual Studio: I was able to compile llvm with MSVC compiler while it failed with clang (some errors on some included Qt .h files). However the llvm libs (both the successfully compiled and the pre-compiled versions) failed on linking to rpcs3 (llvm seems to be compiled as /MD while rpcs3 was compiled as /MT)

[kd-11]

In this case I know why it didn't build, I need to update some preset files. I just ran out of time, hopefully I'll get this done during the holidays.