Avoid redefining _REENTRANT under sanitizers

Switch away from -Wno-macro-redefined which was Clang specific.

Expand the -Wno-macro-redefined usage to MKLIBCSANITIZER

_REENTRANT can be redefined and this is considered as an error.

Enhance the support of LLVM sanitizers

Define _REENTRANT for MKSANITIZER build. This is needed for at least stdio
code. This caused new build issued with duplicated symbols in few places
and rump kernel code picking different code paths borrowed from libc.
Handle all this in one go.

Add bsd.sanitizer.mk to share common code used by programs and libraries.

Switch from realall to beforeinstall target in .syms files. This is more
reliable in MKSANITIZER.

branches: 1.11.2;
Add simple test case for if_nametoindex(3).

branches: 1.10.24; 1.10.26;
Use our own resolv.conf file simplifying the test to not need rump_vfs.
Add debugging on the dns server
One test fails (gethostbyaddr6) why? It runs without rump

Make t_hostent test cases that query the DNS work on systems with no
Internet connectivity, by hijacking DNS queries and /etc/resolv.conf
accesses using librumphijack and providing a minimal DNS server to
answer the queries.

test harness for gethostbyname()/gethostbyaddr() and their internal bits.
XXX[1]: How can we avoid using hard-coded hosts for DNS
XXX[2]: How do we test NIS?

correct spelling of file to clean

branches: 1.6.2; 1.6.8;
atf-ify ether_aton test

Few naive unit tests for the getprotoent(3) family.

Re-add missing -lpthread and fix some structure inializers (not sure how
these ever compiled)

The nsdispatch test belongs in libc/net and not in libc

Move the servent and protoent tests to src/tests/lib/libc/net/ (where
they should have gone initially).

By request, put the getaddrinfo test in tests/lib/libc/net/