Dirty bits not set up on Linux/arm64 with mprotect-vdb in child process #889

Source: master (b93c608)
Link: https://github.com/bdwgc/bdwgc/actions/runs/23057367384/job/66974380699
Host: Ubuntu 24.04/arm64 (20260209.54.1)
Configure options: --disable-shared --enable-cplusplus --enable-gc-assertions
CFLAGS_EXTRA: -D DONT_PROTECT_PTRFREE -D FORCE_MPROTECT_BEFORE_MADVISE -D GC_UNMAPPED_REGIONS_SOFT_LIMIT=120 -D _FORTIFY_SOURCE=2 -O3