[asan] Ignore vDSO on FreeBSD (#76223)

Most asan tests `FAIL` on FreeBSD 14.0/amd64 with
```
==17651==ASan runtime does not come first in initial library list; you should either link runtime to your application or manually preload it with LD_PRELOAD.
```
With `ASAN_OPTIONS=verbosity=2` one sees:
```
==4880==info->dlpi_name = [vdso]	info->dlpi_addr = 0xffffe780
==4880==info->dlpi_name = lib/clang/18/lib/freebsd/libclang_rt.asan-i386.so	info->dlpi_addr = 0x2808a000
```
Ignoring the vDSO as on Linux fixes this.

Tested on `amd64-pc-freebsd14.0`.