"llvm-as is an LLVM IR -> LLVM bitcode assembler not a system
assembler"[1], and therefore should not be linked as "as".
The "as" symlink was removed in 46e5ea5af6 ("llvm*: remove symlinks
to llvm-diff, llvm-as and associated LLVM IR utilities."), but that
was partially reverted by b331c72f03 ("llvm: setup some symlinks for
compatibility with binutils"), which restored a bunch of symlinks that
were incorrectly removed, but also incorrectly restored "as". This
was pointed out[2] at the time but apparently never fixed.
[1]: https://github.com/NixOS/nixpkgs/issues/93523#issue-661663683
[2]: b331c72f03 (commitcomment-40981705)
We were missing symlinks for some programs e.g. strings, which caused
e.g. pkgsLLVM.x264 to fail to build.
Here, I have filled in all the symlinks that LLVM would create if
built with the LLVM_INSTALL_BINUTILS_SYMLINKS option. Where an
existing symlink's target has changed, it's to avoid a double
indirection e.g. strip -> llvm-strip -> llvm-objcopy has because just
strip -> llvm-objcopy.
There's also the related problem that we are creating a as -> llvm-as
symlink, which doesn't make sense, but I'll remove that in a
subsequent commit so that if it somehow breaks something it's easy to
revert just that change.
Fixes: https://github.com/NixOS/nixpkgs/pull/210983
