aarch64: assembler in clang-3.4 ignores the division by two

Values are positive powers of two, so just replace it with right shift.
build: handle library dependencies in configure

Instead of setting FFLIBS in each library Makefile configure
exports FFLIBS-$library in config.mak.
lavf: properly document the distinction between flags and ctx_flags
disable -rpath-link on Solaris

The Solaris -rpath linker option parser is greedy.
build: add Solaris symbol versioning

The Solaris linker does not support globs in linker scripts for
symbol versioning (this is a GNU extension). Let's instead borrow
make_sunver.pl from GCC to make a description file that works
with the Solaris linker.