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 Name Job ID Coverage
  Build
manual build:centos6-x86_64 #5745380
cmake build docker linux manual
passed build:debian10-iwyu #5745377
cmake build docker linux

00:04:03

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

00:05:14

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

00:03:58

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