Change construction of bytecode libraries from producing a single bytecode
file to producing a library containing bytecode files. This gets around the
problem of multiple symbol definitions in the linker if something like
-lc -lc is attempted on the command line. Previously this happened because
the linker would find libc.bc as a "library". It will now find libc.a which
it can simply search for missing symbols instead of linking in wholesale.

llvm-svn: 18425