Fix TSan CI build for develop, cantera (#2991)

## Proposed Changes

The "FATAL: ThreadSanitizer: unexpected memory mapping" message comes
from the TSan runtime. It happens when the kernel's ASLR randomization
is too high for TSan's fixed shadow-memory layout (vm.mmap_rnd_bits=32).
That is the default on recent GitHub runner images and kernels.
The failing step is the bootstrap of ninja, because the Cantera
subproject builds its own ninja when none is on the PATH. The TSan flags
from the job are inherited by that bootstrap. The freshly built ./ninja
is therefore TSan-instrumented and dies on startup with exit status 66,
which gives the Python traceback you see.



## Related Work
*Resolve any issues (bug fix or feature request), note any related PRs,
or mention interactions with the work of others, if any.*



## PR Checklist
*Put an X by all that apply. You can fill this out after submitting the
PR. If you have any questions, don't hesitate to ask! We want to help.
These are a guide for you to know what the reviewers will be looking for
in your contribution.*

- [x] I am submitting my contribution to the develop branch.
- [ ] My contribution generates no new compiler warnings (try with
--warnlevel=3 when using meson).
- [ ] My contribution is commented and consistent with SU2 style
(https://su2code.github.io/docs_v7/Style-Guide/).
- [ ] I used the pre-commit hook to prevent dirty commits and used
`pre-commit run --all` to format old commits.
- [ ] I have added a test case that demonstrates my contribution, if
necessary.
- [ ] I have updated appropriate documentation (Tutorials, Docs Page,
config_template.cpp), if necessary.

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: bigfooted

.github/workflows/regression.yml

@@ -122,6 +122,8 @@ jobs:
         with:
           entrypoint: /bin/rm
           args: -rf install install_bin.tgz src ccache ${{ matrix.config_set }}
+      - name: Lower ASLR entropy for TSan
+        run: sudo sysctl vm.mmap_rnd_bits=28
       - name: Build
         uses: docker://ghcr.io/su2code/su2/build-su2-tsan:261011-1107
         with:
@@ -324,6 +326,8 @@ jobs:
           done
           chmod a+x $BIN_FOLDER/*
           ls -lahR $BIN_FOLDER
+      - name: Lower ASLR entropy for TSan
+        run: sudo sysctl vm.mmap_rnd_bits=28
       - name: Run Tests in Container
         uses: docker://ghcr.io/su2code/su2/test-su2-tsan:261011-1107
         env:

preconfigure.py

@@ -73,6 +73,13 @@ def build_ninja():
             # Specify C++17
             env = os.environ.copy()
             env["CXXFLAGS"] = env.get("CXXFLAGS", "") + " -std=c++17"
+            # ninja is a build tool and must not be instrumented by sanitizers
+            for var in ("CFLAGS", "CXXFLAGS", "LDFLAGS"):
+                env[var] = " ".join(
+                    f
+                    for f in env.get(var, "").split()
+                    if not f.startswith("-fsanitize")
+                )
             subprocess.run(
                 ["python3", "configure.py", "--bootstrap"], cwd=ninjapath, env=env
             )