llvm: Don't install /usr/bin/{gcov,objdump} twice

[ivy]

Summary

Commit c4f08d46c7f7 moved the symlinks for the LLVM binutils from LLVM
itself to the toolchain (usr.bin/clang/toolchain), but did not remove
the links for /usr/bin/gcov and /usr/bin/objdump from the llvm version,
meaning we installed them twice, once in the clang package and once in
the toolchain package.

Remove the links from the llvm version and move the MLINKs to toolchain,
which is where the other MLINKs dwell.

While here, fix toolchain to use the correct build option for llvm-cov,
MK_LLVM_COV.

Fixes: c4f08d46c7f7 ("llvm-*: Move all LLVM_BINUTILS symlinks to toolchain package")
Reported by: jrm
Sponsored by: https://www.patreon.com/bsdivy

[emaste]

usr.bin/clang/llvm-cov/Makefile

3–4

This is implicit if not specified, right?

usr.bin/clang/toolchain/Makefile

39–42

Very minor comment, IMO it would make sense to leave this in alpha order. It probably makes to retire the LLVM_COV option.

[ivy]

rf

[ivy]

usr.bin/clang/llvm-cov/Makefile

3–4

yes, but i was basing this on llvm-ar/Makefile which lists it explicitly... but that's because it installs multiple manpages, so it's not needed here.

usr.bin/clang/toolchain/Makefile

39–42

It probably makes to retire the LLVM_COV option.

i was thinking this as well; it's weird to have a specific option for this and nothing else.

[jrm]

Thanks @ivy.

[emaste]

it's weird to have a specific option for this and nothing else.

Yes. I added it as a transition aid; with GNU gcov long gone it serves no purpose. I'll post a review to get rid of it.