Update intel classic compiler version minimum to 2021.1

[ye-luo]

Proposed changes

Too old intel classic compilers are too painful to deal with. See #4359 CI failure.
Raised to >=2021.1 released in the end of 2020 (as part of oneapi 2021.1)
@williamfgc Update CI will be needed to merge this PR.

What type(s) of changes does this code introduce?

• Build related changes

Does this introduce a breaking change?

• No

What systems has this change been tested on?

bora

Checklist

• Yes. This PR is up to date with current the current state of 'develop'

[ye-luo]

Test this please

[prckent]

OK with this change and the reasoning.

Please mention in the changelog unreleased section. In a later PR we should update readme.md compilers with the current minimums and recommendations.

[williamfgc]

Related to #4326

[prckent]

We should add or even switch to icpx/ icx in our CI. @williamfgc already sulfur has the latest OneAPI compiler (/opt/intel/oneapi/setvars.sh). Is the only reason for monitoring the classic compiler the last few KNL systems?

[ye-luo]

I'm not sure if users switched to icpx already or not. Consider cpu only runs are fast. I would like to keep the classic compiler and add icpx as separate CI variants.

[williamfgc]

Yes, the CPU runs can coexist. One thing this PR does is pulling the plug on the classic compilers available on sulfur. My two cents is to might as well move to OneAPI as recommended by Intel:

Intel® C++ Compiler Classic (icc) is deprecated and will be removed in a oneAPI release in the second half of 2023. Intel recommends that customers transition now to using the LLVM-based [Intel® oneAPI DPC++/C++ Compiler](https://software.intel.com/content/www/us/en/develop/tools/oneapi/components/dpc-compiler.html) (icx) for continued Windows* and Linux* support, new language support, new language features, and optimizations. Note that starting with release 2021.7, macOS* support is limited to Mac* computers with Intel® Processors.  

[ye-luo]

Yes, the CPU runs can coexist. One thing this PR does is pulling the plug on the classic compilers available on sulfur. My two cents is to might as well move to OneAPI as recommended by Intel:

Intel® C++ Compiler Classic (icc) is deprecated and will be removed in a oneAPI release in the second half of 2023. Intel recommends that customers transition now to using the LLVM-based [Intel® oneAPI DPC++/C++ Compiler](https://software.intel.com/content/www/us/en/develop/tools/oneapi/components/dpc-compiler.html) (icx) for continued Windows* and Linux* support, new language support, new language features, and optimizations. Note that starting with release 2021.7, macOS* support is limited to Mac* computers with Intel® Processors.  

The classic compiler is still been maintained as https://www.intel.com/content/www/us/en/developer/articles/release-notes/oneapi-c-compiler-release-notes.html

as long as you install oneapi, classic compilers are still being shipped.

[prckent]

Since OneAPI is already installed, all that is needed is

source /opt/intel/oneapi/setvars.sh intel64
cmake -GNinja -DCMAKE_C_COMPILER=icx -DCMAKE_CXX_COMPILER=icpx -DQMC_MPI=0 ../qmcpack/ # For OneAPI compilers
cmake -GNinja -DCMAKE_C_COMPILER=icc -DCMAKE_CXX_COMPILER=icpc -DQMC_MPI=0 ../qmcpack/ # For Classic compilers

[PDoakORNL]

My #4359 is waiting on this as well.

[williamfgc]

Thank you all, let me try on sulfur and do a PR.

[ye-luo]

Test this please

[ye-luo]

Test this please

[ye-luo]

changelog unreleased section

@prckent Updated