amd64: do not pass -z rodynamic to ld.bfd when building vdso

[kib]

Summary

Apparently newer versions of binutils complain instead of silently ignoring the unknown -z option.

[kib]

Not sure how to make kernel old way (config && make) with cross-toolchain.

Also, what is the idiomatic way to distinguish ld.bfd from ld.lld?

[emaste]

For Makefiles we have bsd.linker.mk that sets LINKER_TYPE, with a similar sort of approach to what you've done here. It uses sed to extract the first line of output from ld -v and then various bits of make magic to examine parts of that.

In ports we check ${/usr/bin/ld:L:tA} == /usr/bin/ld.lld to determine if lld is the default linker (from when it was only so on some archs).

[kib]

In D47176#1075628, @emaste wrote:

For Makefiles we have bsd.linker.mk that sets LINKER_TYPE, with a similar sort of approach to what you've done here. It uses sed to extract the first line of output from ld -v and then various bits of make magic to examine parts of that.

So I am leaving the check as is. IMO it is not worth additional complications to add sed there.

In ports we check ${/usr/bin/ld:L:tA} == /usr/bin/ld.lld to determine if lld is the default linker (from when it was only so on some archs).

[emaste]

One minor comment update

sys/tools/amd64_vdso.sh

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