The MSYS2 CLANG64 toolchain bakes its package-tracker URL
(https://github.com/msys2/MINGW-packages) into the static Windows .exe via
libc++/compiler-rt. The Layer 2 binary string audit flagged it as an
unauthorized URL, failing smoke-windows (both the standard and ui variants)
while Linux smoke stayed green. Add it to ALLOWED_URLS alongside the other
compiler/linker toolchain URLs (gcc.gnu.org, sourceware.org, launchpad).
Add tests/test_security_strings_allowlist.sh as a reproduce-first regression
guard: it reproduces the BLOCKED failure with a binary fixture and includes a
negative control proving a genuinely unauthorized URL is still rejected. Wired
into scripts/test.sh as Step 6.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
