[clang] [Clang][OpenMP] Delay `collapse/ordered` nest walk until instantiation (PR #225052)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `clang` at step 4 "clean-build-dir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/41688

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (clean-build-dir) failure: Delete failed. (failure)
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'lit :: time-tests.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 3
env -u FILECHECK_OPTS "C:\Program Files\Python310\python.exe" Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\utils\lit\lit.py -j1 -D use_normalized_slashes=0 --skip-test-time-recording Inputs/time-tests
# executed command: env -u FILECHECK_OPTS 'C:\Program Files\Python310\python.exe' 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\utils\lit\lit.py' -j1 -D use_normalized_slashes=0 --skip-test-time-recording Inputs/time-tests
# .---command stdout------------
# | -- Testing: 3 tests, 1 workers --
# | PASS: time-tests :: a.txt (1 of 3)
# | PASS: time-tests :: b.txt (2 of 3)
# | PASS: time-tests :: c.txt (3 of 3)
# | 
# | Testing Time: 0.42s
# | 
# | Total Discovered Tests: 3
# |   Passed: 3 (100.00%)
# `-----------------------------
# RUN: at line 4
not ls Inputs/time-tests/.lit_test_times.txt
# executed command: not ls Inputs/time-tests/.lit_test_times.txt
# .---command stderr------------
# | ls: cannot access 'Inputs/time-tests/.lit_test_times.txt': No such file or directory
# `-----------------------------
# RUN: at line 10
env -u FILECHECK_OPTS "C:\Program Files\Python310\python.exe" Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\utils\lit\lit.py -j1 -D use_normalized_slashes=0 --time-tests Inputs/time-tests > Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\Output\time-tests.py.tmp.out
# executed command: env -u FILECHECK_OPTS 'C:\Program Files\Python310\python.exe' 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\utils\lit\lit.py' -j1 -D use_normalized_slashes=0 --time-tests Inputs/time-tests
# note: command had no output on stdout or stderr
# RUN: at line 11
FileCheck --check-prefix=DEFAULT < Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\Output\time-tests.py.tmp.out Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\time-tests.py
# executed command: FileCheck --check-prefix=DEFAULT 'Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\time-tests.py'
# .---command stderr------------
# | Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\time-tests.py:14:12: error: DEFAULT: expected string not found in input
# | # DEFAULT: Slowest Tests (3 of 3):
# |            ^
# | <stdin>:1:1: note: scanning from here
# | -- Testing: 3 tests, 1 workers --
# | ^
# | <stdin>:5:1: note: possible intended match here
# | Slowest Tests (2 of 2):
# | ^
# | 
# | Input file: <stdin>
# | Check file: Z:\b\llvm-clang-x86_64-sie-win\build\utils\lit\tests\time-tests.py
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
...

```

</details>

https://github.com/llvm/llvm-project/pull/225052