oss-fuzz: Always run the check, even on the oss-fuzz platform

oss-fuzz: Always run the check, even on the oss-fuzz platform

It is much harder to determine why we get messages like
    Step #6: Error occured while running fuzz_reg_parse:
    Step #6: /workspace/out/coverage/fuzz_reg_parse: error while loading shared libraries: libavahi-common.so.3: cannot open shared object file: No such file or directory
instead this detects the failure to use RPATH (which is
strictly required instead of the modern RUNPATH)
otherwise.

We do this by creating a new build_samba.sh after renaming
build_samba.sh to do_build.sh because this is what oss-fuzz
runs, meaning we don't need to coordinate a MR there as well.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>