CI: use lld if present (Linux only)

[bcardiff]

EXPORT_CC value can be overridden to disable lld lookup.

• Fixes symbol lookup error #7177 by using lld if present.
• crystallang/crystal:0.32.1-build and crystallang/crystal:0.32.1-i386-build docker images have been updated to include lld-8 according to Install lld-8 as ld.lld on build images crystal-dist#8
• All-required-libraries wiki has been updated to suggest the installation of lld.

[RX14]

How about just

ifeq ($(shell command -v ld.lld >/dev/null && uname -s),Linux)
    CC ?= cc -fuse-ld=lld
endif

then leaving off all the stuff down the page.

This is cleaner, and still lets people override CC in the environment if they wish.

[bcardiff]

I updated the condition but the CC and other vars are not exported automatically

That is also a reason why an EXPORT variable is used somewhere else in the Makefile.

[straight-shoota]

@RX14 Sounds reasonable. But when overriding CC, you'd need to remember to add -fuse-ld=lld explicitly...

[RX14]

Writing export CC works, and is much cleaner.

[RX14]

Please don't merge things before the person who reviewed has had a chance to respond to review followups! Especially when the fix merged wasn't the same as the one suggested.

[straight-shoota]

I agree. I've approved the PR because it seemed fine to me, but I also expected we'd wait for your approval before merging. Maybe there's a communication error and @bcardiff assumed I was sending my approval to merge this immediately.
This has been broken for quite some time so it shouldn't matter whether we merge it a few hours sooner or later.

In general, I'd prefer to wait at least 24 hours before merging a PR to giver others a chance to review and comment. I'm not sure this should go into a policy or something, but it could help to think about that. While it's not a huge issue to apply changes after the PR has been merged via a second PR, it can still cause quite some friction which can be avoided by simply postponing a merge for a few hours. 😉

[bcardiff]

I couldn't make it work with

  CC ?= cc -fuse-ld=lld
  export CC

Adding a @env | grep CC || true to check which the value supposed to be used shows that the default CC=cc is used.

It seems that overriding CC can't be done with ?=.

It also leads to less explicit output. In the current PR the CC="cc -fuse-ld=lld" is displayed explicitly.

Since this is somehow a workaround that might affect some, and using lld is optional I think is better to have an explicit output to allow diagnostic whether lld is used or not.

This trial and error + the approval encourage me to merge it.

Probably I am missing something in my makefile-fu-ness. But I couldn't improve the current solution.

[RX14]

Looks like make has a "prelude" with CC ?= cc in it. So I think the best way to solve this is just to use CC += -fuse-ld=lld and export CC.

I'm not sure about the benefits of having explicit, I personally find it messy. Either way, I appreciate the chance to test my makefile knowledge :P