[llvm] Add the 'initializes' attribute langref and support (PR #84803)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-cuda-l4` running on `cuda-l4-0` while building `llvm` at step 3 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/101/builds/483

Here is the relevant piece of the build log for the reference:
```
Step 3 (annotate) failure: '/buildbot/cuda-build --jobs=' (failure)
...
+ step_summary ''
@@@STEP_SUMMARY_CLEAR@@@
+ echo @@@STEP_SUMMARY_TEXT@@@@
@@@STEP_SUMMARY_TEXT@@@@
+ run ninja check-cuda-simple
+ echo '>>> ' ninja check-cuda-simple
>>>  ninja check-cuda-simple
+ ninja check-cuda-simple
[0/40] cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA && /usr/local/bin/lit -vv -j 1 assert-cuda-11.8-c++11-libc++.test axpy-cuda-11.8-c++11-libc++.test algorithm-cuda-11.8-c++11-libc++.test cmath-cuda-11.8-c++11-libc++.test complex-cuda-11.8-c++11-libc++.test math_h-cuda-11.8-c++11-libc++.test new-cuda-11.8-c++11-libc++.test empty-cuda-11.8-c++11-libc++.test printf-cuda-11.8-c++11-libc++.test future-cuda-11.8-c++11-libc++.test builtin_var-cuda-11.8-c++11-libc++.test test_round-cuda-11.8-c++11-libc++.test
-- Testing: 12 tests, 1 workers --
FAIL: test-suite :: External/CUDA/algorithm-cuda-11.8-c++11-libc++.test (1 of 12)
******************** TEST 'test-suite :: External/CUDA/algorithm-cuda-11.8-c++11-libc++.test' FAILED ********************

/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/timeit-target --timeout 7200 --limit-core 0 --limit-cpu 7200 --limit-file-size 209715200 --limit-rss-size 838860800 --append-exitstatus --redirect-output /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/algorithm-cuda-11.8-c++11-libc++.test.out --redirect-input /dev/null --summary /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/algorithm-cuda-11.8-c++11-libc++.test.time /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/algorithm-cuda-11.8-c++11-libc++
cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA ; /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/algorithm-cuda-11.8-c++11-libc++.test.out algorithm.reference_output-cuda-11.8-c++11-libc++

+ cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA
+ /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/algorithm-cuda-11.8-c++11-libc++.test.out algorithm.reference_output-cuda-11.8-c++11-libc++
/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target: Comparison failed, textual difference between 'C' and 'S'

********************
FAIL: test-suite :: External/CUDA/assert-cuda-11.8-c++11-libc++.test (2 of 12)
******************** TEST 'test-suite :: External/CUDA/assert-cuda-11.8-c++11-libc++.test' FAILED ********************

/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/timeit-target --timeout 7200 --limit-core 0 --limit-cpu 7200 --limit-file-size 209715200 --limit-rss-size 838860800 --append-exitstatus --redirect-output /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/assert-cuda-11.8-c++11-libc++.test.out --redirect-input /dev/null --summary /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/assert-cuda-11.8-c++11-libc++.test.time /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/assert-cuda-11.8-c++11-libc++
cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA ; /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/assert-cuda-11.8-c++11-libc++.test.out assert.reference_output-cuda-11.8-c++11-libc++

+ cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA
+ /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/assert-cuda-11.8-c++11-libc++.test.out assert.reference_output-cuda-11.8-c++11-libc++
/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target: Comparison failed, textual difference between 'e' and 'a'

********************
FAIL: test-suite :: External/CUDA/axpy-cuda-11.8-c++11-libc++.test (3 of 12)
******************** TEST 'test-suite :: External/CUDA/axpy-cuda-11.8-c++11-libc++.test' FAILED ********************

/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/timeit-target --timeout 7200 --limit-core 0 --limit-cpu 7200 --limit-file-size 209715200 --limit-rss-size 838860800 --append-exitstatus --redirect-output /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/axpy-cuda-11.8-c++11-libc++.test.out --redirect-input /dev/null --summary /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/axpy-cuda-11.8-c++11-libc++.test.time /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/axpy-cuda-11.8-c++11-libc++
cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA ; /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/axpy-cuda-11.8-c++11-libc++.test.out axpy.reference_output-cuda-11.8-c++11-libc++

+ cd /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA
+ /buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target /buildbot/cuda-l4-0/work/clang-cuda-l4/build/External/CUDA/Output/axpy-cuda-11.8-c++11-libc++.test.out axpy.reference_output-cuda-11.8-c++11-libc++
/buildbot/cuda-l4-0/work/clang-cuda-l4/build/tools/fpcmp-target: Comparison failed, textual difference between '3' and '2'

********************
PASS: test-suite :: External/CUDA/builtin_var-cuda-11.8-c++11-libc++.test (4 of 12)
********** TEST 'test-suite :: External/CUDA/builtin_var-cuda-11.8-c++11-libc++.test' RESULTS **********
exec_time: 0.0011 
hash: "293d0eb9282156edc5422e7a8c9268e3" 
**********
FAIL: test-suite :: External/CUDA/cmath-cuda-11.8-c++11-libc++.test (5 of 12)

```

https://github.com/llvm/llvm-project/pull/84803