Clean up some ARM asm issues.

1) Allow specification of the section alignment and make the
    default alignment 4 bytes (like the RVCT manual says it should
    be).
   This ensures that linking our ARM asm into a Thumb executable
    won't get the section placed on a 2-byte boundary.
2) Add a linker hint to indicate we don't need an executable stack.
   Otherwise it assumes we do.
3) Stop building and linking to an (empty) armopts object file.
   This is needed to make 2) work, since we include this file, so
    we can't add the linker hint at the end of it, and linking in
    just one object without that hint makes the whole library ask
    for an executable stack.

svn path=/trunk/theora/; revision=18031