Suppress spurious asan errors
Running under clang 11 with asan the test suite generates two groups of spurious errors. Both of them are actually fine, so add some suppression annotations.
With this, the test suite is asan-clean with clang 11. You can verify this by doing
CC=clang CXX=clang++ meson -Db_sanitize=address -Db_lundef=false build cd build ninja test
on a machine with clang 11 installed.