toolchain: Allow building with ASAN and UBSAN

toolchain: Allow building with ASAN and UBSAN

This allows to build all user space with Address sanitizer and undefined
behavior sanitizer. It will automatically add this to the TRAGET_CFLAGS
and TARGET_LDFLAGS of every user space component.

This is only working with gcc 10.X, because the system init process will
mount /proc after it was started and ASAN needs it already earlier and
fails in the versions provided by older compilers.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>