tools/build: Work around broken Clang FreeBSD resource dir logic pre-13

[jrtc27]

Summary

Prior to Clang 13 (e.g. in the Clang 11 present in 13.0-RELEASE), the
resource directory logic for FreeBSD was broken and would not resolve
symlinks, meaning symlinks would only work if in a directory next to the
containing lib directory. Therefore we cannot even use a symlink for
worldtmp, we have to make a wrapper script that execs the real binary
via an absolute path.

Reported by: markj
Fixes: 65f28f63a73d ("tools/build: Create toolchain symlinks for non-absolute compiler/linker")

[markj]

Thanks, this fixes the build error for me.

The diff seems reasonable, though pushing each compiler invocation through this wrapper might have a measurable cost. Though, that only affects the first portion of the world build I think? Would it make sense to limit the workaround to clang before version 13?

[jrtc27]

Limit hack to Clang < 13

[jrtc27]

In D41238#939257, @markj wrote:

Thanks, this fixes the build error for me.

The diff seems reasonable, though pushing each compiler invocation through this wrapper might have a measurable cost. Though, that only affects the first portion of the world build I think? Would it make sense to limit the workaround to clang before version 13?

Depends if you force world to be built with the system compiler or not, as I believe it'll end up using the wrappers in that case. Regardless, it's easy enough to limit it, which seems like a good thing to do for this kind of hack.

[markj]

This version works for me too.