Add support for ICX compiler instead of DPCPP

[minitu]

As of Intel oneAPI 2022, Clang is no longer supported in the compiler toolchain.
This commit fixes the issues that arise from this change (and uses ICX instead of DPCPP).
Build tested on Intel DevCloud with NAMD.
Example build command: ./build charm++ multicore-linux-x86_64 icx -j --with-production

[jszaday]

Charm++ now builds with ICX on a machine that does not have clang++, thanks!

[evan-charmworks]

Is it worth leaving DPCPP support for versions of oneAPI prior to 2022, in case users don't have access to the newest version?

[jszaday]

Is it worth leaving DPCPP support for versions of oneAPI prior to 2022, in case users don't have access to the newest version?

I think icpx has been included with every version of ICX. So, any machine that has icx should have icpx as well. For example, it's present on this lab machine with the 2021 version:

mirzam :: ~ % icpx -v                                                                                                                                                                        
Intel(R) oneAPI DPC++/C++ Compiler 2021.4.0 (2021.4.0.20210924)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/intel/oneapi/compiler/2021.4.0/linux/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Candidate multilib: .;@m64
Selected multilib: .;@m64

[minitu]

@evan-charmworks I think it is cleaner to just have an ICX build available, I believe icpx is basically identical to dpcpp (which is why the DPC++ build of NAMD is also able to use the ICX build of Charm++), and as Justin said icpx (C++ compiler) is available with icx (C compiler). This is also the input from the Intel developers working with me on the NAMD DPC++ porting effort.