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 build:centos6-x86_64 #5745380
linux docker build cmake manual
passed build:debian10-iwyu #5745377
linux docker build cmake

00:04:03

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

00:05:14

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

00:03:58

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