block dlopen of libraries with initial-exec refs to dynamic TLS

block dlopen of libraries with initial-exec refs to dynamic TLS

previously, this operation succeeded, and the relocation results
worked for access from new threads created after dlopen, but produced
invalid accesses (and possibly clobbered other memory) from threads
that already existed.

the way the check is written, it still permits dlopen of libraries
containing initial-exec references to static TLS (TLS in the main
program or in a dynamic library loaded at startup).