IntelLLVM: Add special case for ifx 2021.1 version extraction

The ifx beta versions forgot to define `__INTEL_LLVM_COMPILER`, and
instead define `__INTEL_COMPILER == 201900`.  Add a special case.

Issue: #22120
30 jobs for !6052 with intel-2021 in 5 minutes and 14 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
manual #5745380
linux docker build cmake manual
build:centos6-x86_64
passed #5745377
linux docker build cmake
build:debian10-iwyu

00:04:03

manual #5745381
linux-3.17 linux docker build cmake manual
build:fedora33-ninja
passed #5745379
docker build cmake linux-3.17 linux
build:fedora33-sphinx

00:05:14

passed #5745378
linux-3.17 linux docker build cmake
build:fedora33-tidy

00:03:58

manual #5745383
nonconcurrent xcode-12.4 shell macos cmake manual
build:macos-x86_64-makefiles
manual #5745382
nonconcurrent xcode-12.4 shell macos cmake manual
build:macos-x86_64-ninja
manual #5745384
nonconcurrent msvc-19.28-16.9 vs2019 shell windows cmake manual
build:windows-vs2019-x64-ninja
 
  Test
created #5745385
x11 linux-3.17 linux docker cmake
test:fedora33-ninja
created #5745387
nonconcurrent xcode-12.4 shell macos cmake
test:macos-x86_64-makefiles
created #5745386
nonconcurrent xcode-12.4 shell macos cmake
test:macos-x86_64-ninja
created #5745388
nonconcurrent msvc-19.28-16.9 vs2019 shell windows cmake
test:windows-vs2019-x64-ninja
 
  Test Ext
created #5745391
linux docker cuda-rt cmake
test:cuda10.2-nvidia
created #5745389
linux-3.17 linux docker build cmake
test:debian10-ninja
created #5745390
linux-3.17 linux docker build cmake
test:fedora33-makefiles
created #5745392
linux-3.17 linux docker build cmake
test:fedora33-ninja-multi
created #5745393
concurrent xcode-12.4 shell macos cmake
test:macos-x86_64-xcode
created #5745394
concurrent msvc-19.28-16.9 vs2019 shell windows cmake
test:windows-vs2019-x64
 
  External
passed cdash

passed ghostflow-check-master

passed ghostflow-check-release

passed ghostflow-stager

passed cdash

passed cdash

passed cdash

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager